Jasmonate biosynthesis arising from altered cell walls is prompted by turgor-driven mechanical compression.

Despite the vital roles of jasmonoyl-isoleucine (JA-Ile) in governing plant growth and environmental acclimation, it remains unclear what intracellular processes lead to its induction. Here, we provide compelling genetic evidence that mechanical and osmotic regulation of turgor pressure represents a key elicitor of JA-Ile biosynthesis. After identifying cell wall mutant alleles in KORRIGAN1 (KOR1) with elevated JA-Ile in seedling roots, we found that ectopic JA-Ile resulted from cell nonautonomous signals deriving from enlarged cortex cells compressing inner tissues and stimulating JA-Ile production. Restoring cortex cell size by cell type-specific KOR1 complementation, by isolating a genetic kor1 suppressor, and by lowering turgor pressure with hyperosmotic treatments abolished JA-Ile signaling. Conversely, hypoosmotic treatment activated JA-Ile signaling in wild-type plants. Furthermore, constitutive JA-Ile levels guided mutant roots toward greater water availability. Collectively, these findings enhance our understanding on JA-Ile biosynthesis initiation and reveal a previously undescribed role of JA-Ile in orchestrating environmental resilience.

Inhibition of jasmonate-mediated plant defences by the fungal metabolite higginsianin B.

Infection of Arabidopsis thaliana by the ascomycete fungus Colletotrichum higginsianum is characterized by an early symptomless biotrophic phase followed by a destructive necrotrophic phase. The fungal genome contains 77 secondary metabolism-related biosynthetic gene clusters, whose expression during the infection process is tightly regulated. Deleting CclA, a chromatin regulator involved in the repression of some biosynthetic gene clusters through H3K4 trimethylation, allowed overproduction of three families of terpenoids and isolation of 12 different molecules. These natural products were tested in combination with methyl jasmonate, an elicitor of jasmonate responses, for their capacity to alter defence gene induction in Arabidopsis. Higginsianin B inhibited methyl jasmonate-triggered expression of the defence reporter VSP1p:GUS, suggesting it may block bioactive jasmonoyl isoleucine (JA-Ile) synthesis or signalling in planta. Using the JA-Ile sensor Jas9-VENUS, we found that higginsianin B, but not three other structurally related molecules, suppressed JA-Ile signalling by preventing the degradation of JAZ proteins, the repressors of jasmonate responses. Higginsianin B likely blocks the 26S proteasome-dependent degradation of JAZ proteins because it inhibited chymotrypsin- and caspase-like protease activities. The inhibition of target degradation by higginsianin B also extended to auxin signalling, as higginsianin B treatment reduced auxin-dependent expression of DR5p:GUS. Overall, our data indicate that specific fungal secondary metabolites can act similarly to protein effectors to subvert plant immune and developmental responses.

Wound-Induced Shoot-to-Root Relocation of JA-Ile Precursors Coordinates Arabidopsis Growth.

Multicellular organisms rely on the movement of signaling molecules across cells, tissues, and organs to communicate among distal sites. In plants, localized leaf damage activates jasmonic acid (JA)-dependent transcriptional reprogramming in both harmed and unharmed tissues. Although it has been indicated that JA species can translocate from damaged into distal sites, the identity of the mobile compound(s), the tissues through which they translocate, and the effect of their relocation remain unknown. Here, we found that following shoot wounding, the relocation of endogenous jasmonates through the phloem is essential to initiate JA signaling and stunt growth in unharmed roots of Arabidopsis thaliana. By employing grafting experiments and hormone profiling, we uncovered that the hormone precursor cis-12-oxo-phytodienoic acid (OPDA) and its derivatives, but not the bioactive JA-Ile conjugate, translocate from wounded shoots into undamaged roots. Upon root relocation, the mobile precursors cooperatively regulated JA responses through their conversion into JA-Ile and JA signaling activation. Collectively, our findings demonstrate the existence of long-distance translocation of endogenous OPDA and its derivatives, which serve as mobile molecules to coordinate shoot-to-root responses, and highlight the importance of a controlled redistribution of hormone precursors among organs during plant stress acclimation.