Repression of Jasmonate-Dependent Defenses by Shade Involves Differential Regulation of Protein Stability of MYC Transcription Factors and Their JAZ Repressors in Arabidopsis

Abstract

Reduction of the red/far-red (R/FR) light ratio that occurs in dense canopies promotes plant growth to outcompete neighbors but has a repressive effect on jasmonate (JA)-dependent defenses. The molecular mechanism underlying this trade-off is not well understood. We found that the JA-related transcription factors MYC2, MYC3, and MYC4 are short-lived proteins degraded by the proteasome, and stabilized by JA and light, in Arabidopsis thaliana. Dark and CONSTITUTIVE PHOTOMORPHOGENIC1 destabilize MYC2, MYC3, and MYC4, whereas R and blue (B) lights stabilize them through the activation of the corresponding photoreceptors. Consistently, phytochrome B inactivation by monochromatic FR light or shade (FR-enriched light) destabilizes these three proteins and reduces their stabilization by JA. In contrast to MYCs, simulated shade conditions stabilize seven of their 10 JAZ repressors tested and reduce their degradation by JA. MYC2, MYC3, and MYC4 are required for JA-mediated defenses against the necrotrophic pathogen Botrytis cinerea and for the shade-triggered increased susceptibility, indicating that this negative effect of shade on defense is likely mediated by shade-triggered inactivation of MYC2, MYC3, and MYC4. The opposite regulation of protein stability of MYCs and JAZs by FR-enriched light help explain (on the molecular level) the long-standing observation that canopy shade represses JA-mediated defenses, facilitating reallocation of resources from defense to growth.

Arabidopsis MYC Transcription Factors Are the Target of Hormonal Salicylic Acid/Jasmonic Acid Cross Talk in Response to Pieris brassicae Egg Extract

“…MYC2 accumulates during the day and is degraded during the night (Shin et al, 2012). MYC2, MYC3, and MYC4 are stabilized by light, via the action of red and blue light photoreceptors, and also by JA treatment (Chico et al, 2014). Phosphorylationdependent proteolysis of MYC2 was reported to be essential for its transcriptional activity (Zhai et al, 2013).…”

The RING E3 Ligase KEEP ON GOING Modulates JASMONATE ZIM-DOMAIN12 Stability

“…For JAZ9, it was shown that nuclear localization is dependent on the interaction with the MYC2 transcription factor, and YFP-tagged JAZ9 accumulated in the cytosol in a myc2 mutant (Withers et al, 2012). MYC2, MYC3, and MYC4 are known to be short-lived proteins regulated by proteasomal degradation (Zhai et al, 2013;Chico et al, 2014). GFP-tagged MYC2 is largely removed from the cell in the dark and far-red light (Chico et al, 2014), and MYC2 protein levels oscillate over time under the control of the circadian clock (Shin et al, 2012).…”

PLANT U-BOX PROTEIN10 Regulates MYC2 Stability in Arabidopsis

“…MYC2, MYC3, and MYC4 are very unstable proteins degraded by 26S proteasomes. MYC2 protein levels change in response to signals, e.g., circadian rhythm, methyl jasmonate (MeJA), and specific light conditions (Shin et al, 2012;Zhai et al, 2013;Chico et al, 2014). Dark, far-red light, shade, and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) destabilize MYC2, MYC3, and MYC4, whereas MeJA, red light, and blue light stabilize them.…”

“…Dark, far-red light, shade, and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) destabilize MYC2, MYC3, and MYC4, whereas MeJA, red light, and blue light stabilize them. Differential regulation of MYC2 stability by the change in the ratio of red to far-red light regulates JA-dependent defenses (Chico et al, 2014). TIME FOR COFFEE (TIC) represses MYC2 protein accumulation under the control of circadian clock.…”