Figure Legends
Figure 1. Wired and wireless phytobiome communication. Clonal
plants (right) communicate via physical connections (e.g., stolons and
rhizomes) or VOCs. Plants also communicate via dodder and mycorrhiza
(left). Reciver plants can act as nodes to transfer defense signals
against pests and pathogens to neighboring conspecific and
heterospecific plants. Volatiles and root exudates recived by
neighboring plants modulate receiver plant defense systems, attract
parasitoids and entemopathogens, and induce plant microbiome remodeling
to protect plants against imminent stress conditions.
Figure 2. Illustration of the signal input-transfer-output model
in plant –plant communication. Molecular patterns, volatiles,
and effector proteins of pests and pathogens elicit plant signaling
pathways that promote volatiles emission and root exudation. Plant
signals can be delivered to neighboring plants through the atmosphere or
soil (wireless communication), or transferred through mycorrhiza, fungi,
and odder (wired communication). Signals can be converted to their
active form by receiver plant proteins. Signal perception by neighbor
plants activates signaling pathways and phosphorylation cascades, which
subsequently induce the expression of defense-related proteins and
metabolites. Signal perception also changes the root exudate and
recruits beneficial microbes. MAMPs, microbe-associated molecular
patterns; HAMPs, herbivore-associated molecular patterns; VOCs, volatile
organic compounds; GLVs, green leaf volatiles; BZ, benzoxazinoid; SA,
salicylic acid; MeSA, methyl salicylate; JA, jasmonic acid; MEP,
methylerythritol phosphate; MVA, mevalonic acid; MAPKs,
mitogen-activated protein kinases; TFs, transcription factors.
Figure 3. Signals from neighboring plants modulate signaling
pathways in receiver plants and induce microbiome remodeling. Signals
can be sensed by reciver proteins (e.g., ETR1 sensor for ethylene) or
coverted to active signals [e.g., SABP2 for salicylic acid (SA)].
Signals are transmitted through well-characterized downstream pathways
that may cross-talk with each other. These signaling pathways regulate
defense mechanisms against different groups of attackers and induce
plant microbiome remodeling by changing root exudation, thereby adapting
the plant holobiome to respond to imminent threats. MeSA, methyl
salicylate; SABP2, SA-BINDING PROTEINS 2; NPR,
NON-EXPRESSER OF PR genes; G3P, glycerol-3-phosphate; ETR1, ETHYLENE
RESPONSE 1; EIN2, ETHYLENE INSENSITIVE 2; CTR1, CONSTITUTIVE TRIPLE
RESPONSE 1; ORA59, OCTADECANOID-RESPONSIVE ARABIDOPSIS 59; MeJA, methyl
jasmonate; Med25, Mediator 25; JAZ, JASMONATE ZIM DOMAIN protein;
SCFCOI1, Skp1-Cul1-F-box protein CORONATINE
INSENSITIVE 1; FIT1, FE-DEFICIENCY-INDUCING TRANSCRIPTION FACTOR1; FRO2,
FERRIC REDUCTASE OXIDASE 2; IRT1, IRON-REGULATED TRANSPORTER 1; IAA,
indole-3-acetic acid; AUX1/LAX, AUXIN RESISTANT 1/LIKE AUX1; ALMT1,
ALUMINUM-ACTIVATED MALATE TRANSPORTER; CDPK,
Ca2+-dependent proteinkinases; CIPK, calcineurin B
like proteins (CBL)-interacting protein kinase.