Molecular Mechanism Of Jasmonic Acid Inhibiting The Dark Form Of Arabidopsis Thaliana

The model plant Arabidopsis thaliana emerging from soil needs to experience the growth pattern transition from skotomorphogenesis to photomorphogenesis.Environmental factors (such as light) and endogenous plant hormones play important roles in regulating this kind of switch. Until now, whether jasmonate is involved in the regulation of photomorphogenesis remains unknown.In this study, we found that jasmonate inhibits skotomorphogenesis in Arabidopsis,including suppressing hypocotyl elongation and stimulating cotyledon opening in etiolated seedlings. By observing the phenotypes of some jasmonate signaling mutants,we demonstrated that jasmonate receptor COI1, JAZ proteins, and bHLH transcription factor MYC2 are involved in this process.Exogenous jasmonate treatment partially rescues photoreceptor mutants,including cry1 cry2,phyA phyB, under blue light or red light respectively, suggesting that jasmonate activates light responses downstream of photoreceptors.COP1 is critical for maintaining skotomorphogenesis. In darkness, cop1 mutants exhibit short hypocotyls and opened cotyledons. COP1 targets a number of photomorphogenesis-promoting transcription factors (such as HY5,HYH, LAF1,HFR1, PAR1, PAR2) to degradation through the 26S proteasome for preventing photomorphogenesis. We found that jasmonate could not suppress cop1 hypocotyl elongation in the dark, and promotes the HY5 and PAR1/2 protein accumulation in a COP 1-dependent manner. Both hy5-ks50 and hy5 hyh loss-of-function mutants display reduced sensitivity to jasmonate in hypocotyl elongation and cotyledon unfolding phenotypes. Plants overexpressing either PARI or PAR2 are hypersensitive to jasmonate during the hypocotyl elongation response. Knockdown of both PAR1and PAR2 (PAR-RNAi) did not result in a remarkable difference compared with wild-type plants,suggesting that PAR1 and PAR2 are positive regulators of jasmonate-inhibited hypocotyl elongation. Jasmonate suppresses COP1 activity through at least two distinct mechanisms: decreasing COP1 protein accumulation in the nucleus and reducing the physical interaction between COP1 and its activator SPA1.We further took genome-wide mRNA expression analysis to study the signaling interaction between jasmonate and light and revealed a jasmonate-light co-regulated and cop1-dependent transcriptome, which is enriched for auxin-responsive genes and genes participating in cell wall modifications, suggesting that jasmonate can elicit some light- signaling related gene expression changes.In conclusion, our work shows that jasmonate inhibits skotomorphogenesis in Arabidopsis. Photomorphogenesis negative regulator COP 1 and positive regulators HY5 and PAR1/2 are required for this process. Jasmonate suppresses COP1 activity to stabilize COP1 targets, thereby inhibiting hypocotyl elongation and stimulating cotyledon unfolding in etiolated Arabidopsis seedlings. Jasmonate treatment also elicits the expression of a set of light-responsive genes in etiolated seedlings.