The Molecular Mechanism Of Cross-talking Between Light-and Phytohormones Strigolactone-and Jasmonate-signaling

The seedlings morphogenesis including hypocotyl elongation and cotyledon expansion, andanthocyanin and chlorophyll accumulation are critical processes for plant growth and development.Light signal is a key environmental cue, which regulates morphogenesis mainly throughphotoreceptors like cryptochromes and phytochromes. The phytohormones also play importantroles in regulating these processes. The novel shoot branching phytohormone, strigolatones， havebeen reported to participate in hypocotyl growth regulation in Arabidopsis. Moreover，the stressresponsive phytochormone, jasmonate, is previous demonstrated in promoting anthocyaninaccumulation. So, how light signal crosstalks with these two phytohormones signaling inregulation of seedlings morphogenesis is largely unknown.By combination of genetic and molecular biology analysis, our study mainly explorers themechanism of interplays between light-and phytohormones-signaling in Arabidopsis.We firstly study the molecular basis of light signaling interaction with strigolatone signalingin regulating hypocotyl eloangation. We achieved the results as follows. We demonstrate that theinhibition of hypocotyl elongation by low concentrations of strigolactone analog GR24(≤10μM)is dependent on cryptochrome and phytochrome signaling pathways. The photoreceptor mutantscry1cry2, phyA, and phyB are hyposensitive to GR24under the respective monochromatic lightconditions, while the mutants of negative photomophogenic factors cop1and pif1pif3pif4pif5(pifq) quadruple mutants are sensitive to GR24even in darkness. Genetic studies indicate that theresponsiveness of cop1to GR24in darkness is dependent on HY5and MAX2, while that of pifq islargely independent of HY5. Further studies demonstrate that GR24constitutively up-regulatesHY5expression in the dark and light, whereas GR24-promoted HY5protein accumulation is light-and cryptochrome and phytochrome photoreceptors-dependent. These results suggest that the lightdependency of strigolactone regulation of hypocotyl elongation is likely mediated throughMAX2-dependent promotion of HY5expression, light-dependent accumulation of HY5, and PIF-regulated components.The second part of this study reveales the molecular mechanism for regulation of anthocyaninbiosynthesis by light and jasmonate signaling. Jasmonate regulates anthocyanin biosynthesis bypromoting the transcriptional activities of R2R3MYB transcriptional factors including MYB75andMYB90. Light signal influences anthocyanin accumulation by releasing the degradation of HY5,HFR1etc from COP1-dependent26S proteosome pathway. This study shows that jasmonatesignaling enhance seedlings anthocyanin accumulation dependent on phytochrome andcryptochrome photoreceptors. The genetic relationship between MYBs and COP1indicate thatMYBs act downstream of COP1in promoting anthocyanin biosynthesis. MYB75over-expressionin hy5mutant background can rescue the anthocyanin-reducing phenotype of hy5, which suggestsMYB75is epigynous to HY5in regulation of anthocyanin biosynthesis. We further analyze theMYB75protein level by constructing the transgenic lines of35S::FLAG-MYB75. Results showthat MYB75protein increases when exposing to light. While in darkness, MYB75protein isdegraded through26S proteosome pathway in COP1dependent manner. Yeast two hybrid andco-localizition assays indicate that COP1directly interacts with MYB75and MYB90in vivo.Taken together, this study suggest light signaling crosstalk with jasmonate signaling in regulationanthocyanin biosynthesis by releasing the COP1-mediated degradation of MYB75.These results demonstrate light signal interplay with strigolatone and jasmonate signaling inregulating hypocotyls elongation and anthocyanin biosynthesis in transcriptional andpost-transcriptional manner respectively.