Phytochrome is a red/far-red photoreceptor that regulates various plant developmental processes. Red light activated phytochrome translocates into the nucleus to inhibit negative regulator of photomorphogenesis, Phytochrome-Interacting Factors (PIFs). PIFs are bHLH transcription factors that regulate seed germination, hypocotyl elongation, chlorophyll biosynthesis, senescence and flowering etc. Various molecular functions of PIFs are well discovered through previous researches, but it is still unclear that the exact role of phy-PIF signaling in plastid differentiation of seedling stage.
In this study, I discovered downstream components of phy-PIF signaling to regulate amyloplast conversion through forward-genetic methods. I did EMS mutagenesis of SCR:PIF1/pifQ to find suppressor mutants of endodermis-specific PIF1 on endodermal amyloplast conversion. I selected mutants by observation of hypocotyl gravitropism phenotype such as hypocotyl standing percentage and amyloplast staining. I found 28 candidates through mutant screening, and starchless mutants such as pgm1, adg1 and isa1 are included in those mutant candidates.
As an independent study, I discovered JOGAKs (JOGs) which are direct targets of PIFs through reverse-genetic methods, microarray and ChIP-chip. 4-week LD grown jog1jog3 double mutant shows high chlorophyll level while JOG1 and JOG3 OX show much low chlorophyll level in a whole stage. I discovered that JOG1/3 inhibits chlorophyll synthestic genes as well as chloroplast component genes through GLK1/2 transcription factors. JOG1/3 binds to GLK1/2 in vitro, and they regulate overall chloroplast-related genes in opposite way of GLK1/2. I suggest that phy-PIF-JOG signaling regulates chloroplast apparatus through GLK1/2.
Through these genetic approaches, I could find a few downstream factors of phy-PIF signaling in plastid differentiation.