BioProject

Jasmonates are key regulators of the balance between defence and growth in plants. More...

Jasmonates are key regulators of the balance between defence and growth in plants. However, the molecular mechanisms by which activation of defences reduces growth are not yet understood. Here, we analyze the role of MYC transcription factors (TFs) and JA in photomorphogenic growth. We found that multiple myc mutants share light-related phenotypes with mutants of the phytochrome B photoreceptor, regarding seed germination and hypocotyl growth. Over-expression of MYC2 in a phyB background partially suppressed its long hypocotyl phenotype. We show that the activity of MYC TFs is partially independent of COI1 and that JA inhibition of hypocotyl growth acts through alteration of auxin homeostasis and is partially independent of the classical JA signalling pathway. Transcriptomic analysis of multiple myc mutants confirmed that MYCs are required for full expression of R-light regulated genes, including the master regulator HY5. ChIP-Seq analyses revealed that MYC2 and MYC3 directly bind to the promoter of HY5 and that HY5 gene expression and protein levels are compromised in multiple myc mutants. Moreover, MYC2 and MYC3 share a high amount of direct targets with PIFs, and have an opposite effect on gene expression of these targets. Altogether, our results pinpoint MYCs as photomorphogenic TFs that regulate phytochrome responses by regulating PIFs targets and activating HY5 expression. This has important implication to understand the trade-off between growth and defence, since the same TFs that activate defence responses are photomorphogenic growth regulators. Overall design: Two experimental conditions: Triple myc2,3,4 mutant vs Col-0 plants grown under white light (WL) conditions; andTriple myc2,3,4 mutant vs Col-0 plants supplemented with monochromatic Far red light. Less...