5.5 Other signaling mechanisms
Another key area for future research is small RNAs, which can play important regulatory roles in plant responses to stress. Work done in Arabidopsis has indicated microRNAs (miRNA) are involved in response to phosphate stress, while miRNAs are responsive to cold stress inBrachypodium distachyon (Fujii et al., 2005; Chiou et al., 2006; Zhang et al., 2009). Gene expression analysis in soybean indicates miRNAs play a role in mediating drought and fungal stress (soybean rust fungus) through modulation of regulation of ROS (Kulcheski et al., 2011). Small interfering RNAs (siRNAs), including nat-siRNAs, have also been shown to regulate both abiotic and biotic stress responses in Arabidopsis and rice (Atkinson & Urwin, 2012). Additionally, small RNAs play a role in plant developmental processes, including flowering time and fertility (Atkinson & Urwin, 2012), indicating their key role at the intersection of plant defense and productivity. This indicates small RNAs would be a viable future area of research to understand plant responses to combined stresses. Additional pathways of interest for future work include genes involved in calcium signaling, mitochondrial functions, vesicle trafficking, apoptosis, as well as pathway regulation of the hyper-sensitivity response, epigenetic regulation, and the role of cis -regulatory elements (CREs) (Fujita et al., 2006; Atkinson & Urwin, 2012; Kissoudis et al., 2014; Nejat & Mantri, 2017; Shigenaga et al., 2017; Romero-Puertas et al., 2021; Singh et al., 2021; Zarratini et al., 2021).
ADDRESSING GAPS IN OUR KNOWLEDGE
In addition to the future research targets outlined above, additional experimental approaches and techniques could be used to enhance our understanding of crosstalk and trade-offs of plant biotic and abiotic stress responses imposed by climate change.
I. Experiments in both controlled environments and in the field that address realistic depictions of future climate. This includes evaluating regional versus global impacts of specific abiotic and biotic stress interactions. By assessing climate scenarios that have resolution at the regional scale, we can more accurately predict the impacts of future growing conditions on crops of interest (Leisner, 2020), as well as gain a better understanding of the mechanisms involved in crop responses to stress combinations at the physiological, molecular, and genetic level (Rivero et al., 2022). Additionally, knowledge gaps related to different plant pathosystems should be addressed, to expand our understanding to specific plant-pathogen interactions under future climate scenarios. II. Modeling and predictive tools for decision making. Precision agriculture is a large field that is focused on using advanced robotics, image analysis, and mapping technologies to improve a farmer’s ability to make decisions regarding soil and water supplies in real-time (Cisternas et al., 2020). This can help make decision support tools available for stakeholders to manage plant responses to climate change. We need to increase efforts to utilize the same concepts of precision agriculture to the management of pathogen infection. This includes predicting climate change effects on pathogen emergence using artificial intelligence and giving decision-makers automated analyses of risk to make educated decisions during the growing season (Garrett et al., 2022). III. Interdisciplinary research to tackle complex problems. We need to take a systems biology approach to gain a complete picture of how plants interact with their changing environment. This includes addressing issues of physiological responses of plants to their environment, how these are linked to changes at the genetic level, and how these changes at the whole plant level might translate into ecological impacts in natural or agroecosystems. Additionally, links between belowground factors (soil composition, rhizosphere interactions) and the plant microbiome (Hacquard et al., 2022) will be key to increasing plant health, defense, and productivity under future climate conditions.
CONCLUSIONS
Plants must adapt and respond to an ever-changing environment. Human influence has led to increased CO2 in our atmosphere, warming of our land, and changes in precipitation patterns. These changes to our global ecosystem will also lead to changes in the prevalence and virulence of plant pathogens, and plant herbivores. To ensure sustainable future food production, we must understand the crosstalk and trade-offs resulting from combined abiotic and biotic stress impacts on plant growth and defense. Outcomes from experiments where plants are exposed to multiple stresses are often unique from the individual stress alone, especially at the level of gene expression. There is, however, significant crosstalk among these stresses, with key hubs of integration of signals across stresses involving transcription factors, hormones (ABA, SA, JA), ROS, small RNAs, and MAPK cascades. These are key targets for future research efforts. More combinatorial stress work is needed in the future to understand growth and defense trade-offs and crosstalk among plant biotic and abiotic stress responses. This work should incorporate realistic depictions of future climate, leverage interdisciplinary teams of researchers, and employ advanced tools in precision agriculture and predictive tools for decision making (Fig. 1 ).