How variations in carbon supply affect wood formation remains poorly understood in particular in mature forest trees. To elucidate how carbon supply affects carbon allocation and wood formation, we attempted to manipulate carbon supply to the cambial region by phloem girdling and compression during the mid- and late-growing season and measured effects on structural development, CO2 efflux, and nonstructural carbon reserves in stems of mature white pines. Wood formation and stem CO2 efflux varied with location relative to treatment (i.e., above or below the restriction). We observed up to twice as many tracheids formed above versus below the treatment after the phloem transport manipulation, whereas cell-wall area decreased only slightly below the treatments, and cell size did not change relative to the control. Nonstructural carbon reserves in the xylem, needles, and roots were largely unaffected by the treatments. Our results suggest that low and high carbon supply affects wood formation, primarily through a strong effect on cell proliferation, and respiration, but local nonstructural carbon concentrations appear to be maintained homeostatically. This contrasts with reports of a decoupling of source activity and wood formation at the whole-tree or ecosystem level, highlighting the need to better understand organ-specific responses, within-tree feedbacks, as well as phenological and ontological effects on sink-source dynamics.
While many phenylpropanoid pathway-derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID-4-HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad-spectrum resistance in higher plant without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signaling and pathogenesis-related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root-knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid-degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity.
Early signaling events in response to elicitation include reversible protein phosphorylation and re-localization of plasma membrane (PM) proteins. Oligogalacturonides (OGs) are a class of Damage-Associated Molecular Patterns (DAMPs) that act as endogenous signals to activate the plant immune response. Previous data on early phosphoproteome changes in Arabidopsis thaliana upon OG perception uncovered the immune-related phospho-regulation of several membrane proteins, among which PCaP1, a PM-anchored protein with actin filament-severing activity, was chosen for its potential involvement in OG- as well as flagellin-triggered responses. Here we demonstrate that PCaP1 is required for late, but not early, responses induced by OGs and flagellin. Moreover, pcap1 mutants, unlike the wild type, are impaired in the recovery of full responsiveness to a second treatment with OGs performed 24 h after the first one. Localization studies on PCaP1 upon OG treatment in plants expressing a functional PCaP1-GFP fusion under the control of PCaP1 promoter revealed fluorescence on the PM, organized in densely packed punctate structures, previously reported as microdomains. Fluorescence was found to be associated also with endocytic vesicles, the number of which rapidly increased after OG treatment, suggesting both an endocytic turnover of PCaP1 for maintaining its homeostasis at the PM and an OG-induced endocytosis.
Little is known about the sources and age of C respired from tree roots. Previous research in tree stems has identified two functional pools of non-structural carbohydrates (NSC): an ‘active’ pool supplied directly from canopy photo-assimilates that supports metabolism and a ‘stored’ pool used when fresh C supplies are limited. We compared the C isotope composition of water soluble NSC and respired CO2 for aspen roots (Populus tremula hybrids) that were cut off fresh C supply via stem-girdling and prolonged incubation of excised roots. We used bomb radiocarbon to estimate the time elapsed since C fixation for respired CO2, water-soluble C, and structural α-cellulose. While freshly excised roots respired CO2 with mean age <1 yr, within a week the age increased to 1.6-2.9 yr. Freshly excised roots from trees girdled ~3 months previously had similar respiration rates and NSC stocks as un-girdled trees, but respired older C (~1.2 yr). We estimate the NSC in girdled roots must be replaced 5-7 times by reserves remobilized from root-external sources. Using a mixing model and observed correlations between Δ14C of water-soluble C and α-cellulose, we estimate ~30% of C is ‘active’ (~5 mg C g-1).
Phosphate (Pi) and jasmonic acid (JA) play critical roles in plant growth and development. In particular, crosstalk between JA and Pi starvation signaling has been reported to mediate insect herbivory resistance in dicot plants. However, its roles and mechanism in monocot-bacterial defense systems remain obscure. Here, we report that Pi starvation in rice activates the JA signaling and enhances resistance to Xanthomonas oryzae pv. oryzae (Xoo) infection. The direct regulation of OsPHR2 on the OsMYC2 promoter was confirmed by yeast one-hybrid, electrophoretic mobility shift, dual-luciferase, and chromatin immunoprecipitation assays. Molecular analyses and infection studies using OsPHR2-Ov1 and phr2 mutants further demonstrated that OsPHR2 enhances JA response and antibacterial resistance via transcriptional regulation of OsMYC2 expression, indicating a positive role of OsPHR2-OsMYC2 crosstalk in modulating the JA response and Xoo infection. Genetic analysis and infection assays using myc2 mutants revealed that Pi starvation-induced JA signaling activation and consequent Xoo resistance depends on the regulation of OsMYC2. Together, these results reveal a clear interlink between Pi starvation signaling and the JA signaling in monocot plants, and provide new insight into how plants balance growth and defense by integrating nutrient deficiency and phytohormone signaling.
CO2 responsive CCT protein (CRCT) is a positive regulator of starch synthesis related genes such as ADP-glucose pyrophosphorylase large subunit 1 and starch branching enzyme I particularly in the leaf sheath of rice (Oryza sativa L.). The promoter GUS analysis revealed that CRCT expressed exclusively in the vascular bundle, whereas starch synthesis related genes were expressed in different sites such as mesophyll cell and starch storage parenchyma cell. However, the chromatin immunoprecipitation (ChIP) using a FLAG-CRCT overexpression line and subsequent qPCR analyses showed that the 5’-flanking regions of these starch synthesis-related genes tended to be enriched by ChIP, suggesting that CRCT can bind to the promoter regions of these genes. The monomer of CRCT is 34.2 kDa, however CRCT was detected at 270 kDa via gel filtration chromatography, suggesting that CRCT forms a complex in vivo. Immunoprecipitation and subsequent MS analysis pulled down several 14-3-3-like proteins. A yeast two-hybrid analysis and bimolecular fluorescence complementation assays confirmed the interaction between CRCT and 14-3-3-like proteins. Although there is an inconsistency in the place of expression, this study provide important findings regarding the molecular function of CRCT to control the expression of key starch synthesis-related genes.
Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating interspecific and intraspecific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin vs. non-kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behavior, allelochemical production, and soil microbial community composition, as well as carbon and nitrogen partitioning in the weeds. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non-kin mixtures. The effect was driven by kin recognition that induced altered root placement, established similar soil microbial communities, and altered weed carbon and nitrogen partitioning. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighboring collaborators (kin) or competitors and then adjust their growth, competitiveness and chemical defense accordingly.
Since the first description of phloem sap composition nearly 60 years ago, it is generally assumed that phloem sap does not contain nitrate and that there is little or no backflow of nitrate from shoots to roots. While it is true that nitrate can occasionally be absent from phloem sap, there is now substantial evidence that phloem can carry nitrate and furthermore, transporters involved in nitrate redistribution to shoot sink organs and roots have been found. This raises the question of why nitrate may or may not be present in phloem sap, why its concentration is generally kept low, and whether plant shoot-root nutrient cycling also involves nitrate. We propose here that phloem sap nitrate is not only an essential component of plant nutritional signaling but also contributes to physical properties of phloem sap and as such, its concentration is controlled to ensure proper coordination of plant development and nutrient transport.
Atmospheric and climate change will expose tropical forests to conditions they have not experienced in millions of years. To better understand the consequences of this change we studied photosynthetic acclimation of the neotropical tree species Tabebuia rosea to combined 4°C warming and twice-ambient (800 ppm) CO2. We measured temperature responses of the maximum rates of ribulose 1,5-bisphosphate carboxylation (VCMax), photosynthetic electron transport (JMax), net photosynthesis (PNet), and stomatal conductance (gs), and fitted the data using a probabilistic Bayesian approach. To evaluate short-term acclimation plants were then switched between treatment and control conditions and re-measured after 1–2 weeks. Consistent with acclimation, the optimum temperatures (TOpt) for VCMax, JMax and PNet were 1–5°C higher in treatment than in control plants, while photosynthetic capacity (VCMax, JMax, and PNet at TOpt) was 8–25% lower. Likewise, moving control plants to treatment conditions moderately increased temperature optima and decreased photosynthetic capacity. Stomatal density and sensitivity to leaf-to-air vapor pressure deficit were not affected by growth conditions, and treatment plants did not exhibit stronger stomatal limitations. Collectively, these results illustrate the strong photosynthetic plasticity of this tropical tree species as even fully-developed leaves of saplings transferred to extreme conditions partially acclimated.
Opportunistic diversification has allowed ferns to radiate into epiphytic niches in angiosperm dominated landscapes. However, our understanding of how ecophysiological function allowed establishment in the canopy and the potential transitionary role of the hemi-epiphytic life form remain unclear. Here, we surveyed 39 fern species in Costa Rican tropical forests to explore epiphytic trait divergence in a phylogenetic context. We examined leaf responses to water deficits in terrestrial, hemi-epiphytic, and epiphytic ferns and related these findings to functional traits that regulate leaf water status. Epiphytic ferns had reduced xylem area (-63%), shorter stipe lengths (-56%), thicker laminae (+41%), and reduced stomatal density (-46%) compared to terrestrial ferns. Epiphytic ferns exhibited similar turgor loss points, higher osmotic potential at saturation, and lower tissue capacitance after turgor loss than terrestrial ferns. Overall, hemi-epiphytic ferns exhibited traits that share characteristics of both terrestrial and epiphytic species. Our findings clearly demonstrate the prevalence of water conservatism in both epiphytic and hemi-epiphytic ferns, via selection for anatomical and structural traits that avoid leaf water stress. Even with likely canalized physiological function, adaptations for drought avoidance have allowed epiphytic ferns to successfully endure the stresses of the canopy habitat.
Effects of K deficiency have been investigated for several decades and recently, progress has been made in identifying metabolomics signatures thereby offering potential to monitor the K status of crops in the field. However, effects of low K conditions could also be due to the antagonism with other nutrients like calcium (Ca) and the well-known biomarker of K deficiency, putrescine, could be a response to Ca/K imbalance rather than K deficiency. We carried out experiments in sunflower grown at either low or high K, at high or low Ca, with or without putrescine added to the nutrient solution. Using metabolomics and proteomics analysis, we show that a significant part of the low-K response such as lower photosynthesis and N assimilation, is due to calcium and can be suppressed by low Ca conditions. Putrescine addition tends to restore photosynthesis and N assimilation but but aggravates the impact of low-K conditions on catabolism. We conclude that (i) effects of K deficiency can be partly alleviated by the use of low Ca and not only by K fertilization, and (ii) in addition to its role as a metabolite, putrescine participates in the regulation of the content in enzymes involved in carbon primary metabolism.
Several species of soil free-living saprotrophs can sometimes establish biotrophic symbiosis with plants, but the basic biology of this association remains largely unknown. Here, we investigate the symbiotic interaction between a common soil saprotroph, Clitopilus hobsonii (Agaricomycetes), and the American sweetgum (Liquidambar styraciflua). Notably, the colonized root cortical cells contain numerous microsclerotia-like structures. Fungal colonization led to increased plant growth and facilitated potassium uptake, particularly under potassium limitation (0.05 mM K+). The expression of plant genes related to potassium uptake is not altered during symbiosis, whereas the transcripts of three fungal genes encoding ACU, HAK, and SKC involved in K+ nutrition is found in colonized roots. We confirmed the K+ influx activities by expressing the ChACU and ChSKC genes into a yeast K+-uptake-defective mutant. Upregulation of the ChACU under 0.05 mM K+ and no K+ conditions was demonstrated in planta and in vitro compared to normal condition (5 mM K+). In addition, colonized plants displayed a larger accumulation of soluble sugars under 0.05 mM K+. The present study highlights that potassium limitation promotes this novel tree-fungus symbiosis mainly through a reciprocal transfer of additional carbon and potassium to both partners, and the role of dual soil saprotroph/symbiotroph in tree nutrition.
Embolism spreading in dehydrating angiosperm xylem is driven by gas movement between embolised and sap-filled conduits. Here, we examine how proximity to pre-existing embolism and hydraulic segmentation affect embolism propagation. Based on the optical method, we compared xylem embolism resistance between detached leaves and leaves attached to branches, and between intact leaves and leaves with cut minor veins for six species. Moreover, we directly compared the optical and pneumatic method on detached leaves. Embolism resistance of detached leaves was significantly lower than leaves attached to stems, except for two species with all vessels ending in their petioles. Cutting of minor veins showed limited embolism spreading in minor veins near the cuts prior to major veins. Moreover, there was strong agreement in embolism resistance between the optical and pneumatic method, with minor differences occurring during early stages of embolism formation. We conclude that embolism resistance may represent a relative trait, depending on the proximity and connectivity to pre-existing embolism as a gas source. Since embolism formation may not rely on a certain pressure difference threshold between functional and embolised conduits, we suggest that embolism is facilitated by pressure-driven gas diffusion, while hydraulic segmentation can prevent embolism propagation by reducing gas diffusion.
Nicotinamide-adenine dinucleotide (NAD) is involved in redox homeostasis and acts as a substrate for NADases, including poly (ADP-ribose) polymerases (PARPs) that add poly (ADP-ribose) polymers to proteins and DNA, and sirtuins that deacetylate proteins. Nicotinamide, a biproduct of NADases increases circadian period in both plants and animals. In mammals, the effect of nicotinamide on circadian period might be mediated by the PARPs and sirtuins because thy directly bind to core circadian oscillator genes. We have investigated whether PARPs and sirtuins contribute to the regulation of the circadian oscillator in Arabidopsis. We found no evidence that PARPs and sirtuins regulate the circadian oscillator of Arabidopsis or are involved in the response to nicotinamide. RNA-seq analysis indicated that PARPs regulate the expression of only a few genes, including FLOWERING LOCUS C. However, we found profound effects of reduced sirtuin 1 expression on gene expression during the day but not at night, and an embryo lethal phenotype in knockouts. Our results demonstrate that PARPS and sirtuins are not associated with NAD regulation of the circadian oscillator and that sirtuin 1 is associated with daytime regulation of gene expression.
ants share the phytobiome with other members of the ecological community by sharing their physiology. The phytobiome is a collective ecological entity that senses external and internal stimuli via its member’s sensing apparatus (senome). The activated senome generates intercellular, and intra- and inter-organismal signals that induce genetically and epigenetically dependent modifications of phytobiome member transcriptomes. Ultimately, these genetic modifications alter the phenotypes of the collective phytobiome members. Mycorrhiza, epiphytic fungi, and dodder can physically transfer signals between kin and non-kin plants. Phytobiome members can release infochemicals by themselves, or modify plant volatile emissions and root exudates to act as signals for plant–plant interactions. These signals can change plant physiology and induce holobiont updates in receiver plants via a facilitative or competitive mechanism. Receiver plants eavesdrop on phytobiome cues and signals to anticipate responses to unfolding challenges. An emerging body of information in plant–plant interactions through inter-kingdom communication can be exploited in integrated crop management under field conditions. However, a holistic view is crucial for the manipulation of complex systems, such as the phytobiome, to avoid potential butterfly effects.
Trees’ total amount of nonstructural carbohydrate (NSC) stores and the proportion of these stores residing as insoluble starch are vital traits for individuals living in variable environments. However, our understanding of how stores vary in response to environmental stress is poorly understood as the genetic component of storage is rarely accounted for in studies. Here, we quantified variation in NSC traits in branch samples taken from over 600 clonally transplanted black cottonwood (Populus trichocarpa) trees grown in two common gardens. We found heritable variation in both total NSC stores and the proportion of stores in starch (H2TNC = 0.19, H2PropStarch = 0.31), indicating a substantial genetic component of variation. In addition, we found high amounts of plasticity in both traits in response to cold temperatures and significant genotype-by-environment (GxE) interactions in the total amount of NSC stored (54% of P is GxE). This finding of high GxE indicates extensive variation across trees in their response to environment, which may explain why previous studies of carbohydrate stores’ responses to stress have failed to converge on a consistent pattern. Overall, we found high amounts of environmental and genetic variation in NSC storage concentrations, which may bolster species against future climate change.
Plant growth depends on the diurnal regulation of cellular processes, but it is not well understood if and how transcriptional regulation controls diurnal fluctuations at the protein-level. Here we report a high-resolution Arabidopsis thaliana (Arabidopsis) leaf rosette proteome acquired over a 12 h light : 12 h dark diurnal cycle and the phosphoproteome immediately before and after the light-to-dark and dark-to-light transitions. We quantified nearly 5000 proteins and 800 phosphoproteins, of which 288 fluctuated in their abundance and 226 fluctuated in their phosphorylation status. Of the phosphoproteins, 60% were quantified for changes in protein abundance. This revealed six proteins involved in nitrogen and hormone metabolism that had concurrent changes in both protein abundance and phosphorylation status. The diurnal proteome and phosphoproteome changes involve proteins in key cellular processes, including protein translation, light perception, photosynthesis, metabolism and transport. The phosphoproteome at the light-dark transitions revealed the dynamics at phosphorylation sites in either anticipation of or response to a change in light regime. Phosphorylation site motif analyses implicate casein kinase II and calcium/calmodulin dependent kinases among the primary light-dark transition kinases. The comparative analysis of the diurnal proteome and diurnal and circadian transcriptome established how mRNA and protein accumulation intersect in leaves during the diurnal cycle of the plant.