| Summary: | 碩士 === 國立臺灣大學 === 植物科學研究所 === 98 === Far-red insensitive 219 (FIN219) was previously shown to be involved in phytochrome A-mediated far-red (FR) light signaling in Arabidopsis. Far-red Elongated Hypocoty l (FHY1) is a positive regulator and required for FR-regulated nuclear accumulation of phyA. Previous study indicated that the fin219/fhy1 transheterozygote exhibited a long hypocotyl phenotype in FR similar to their homozygous parental mutants, suggesting that fin219 and fhy1 mutants are nonallelic noncomplementary. However the molecular mechanism underlying the genetic interaction of FIN219 and FHY1 remains largely unknown. We use molecular genetics and cell biology approaches to understand their interaction and expression patterns in Arabidopsis. Firstly, we crossed the T-DNA insertion mutants of fin219 null and fhy1-T to generate a homozygous double mutant, which further exhibited an enhanced far-red insensitive phenotype compared to its respective parental mutants in weak FR, but same as fhy1-T in strong FR. In phenotypic analysis of transgenic plants, we found that over-expression of FIN219 or FHY1 in fhy1-1 or fin219 null respectively can partially rescue respective long-hypocotyl phenotype. Hence, we hypothesize that FIN219 may interact with FHY1. By using yeast two-hybrid and bimolecular fluorescence complementation approaches, we demonstrated that they interacted with each other in the nuclei only, and also in both the nuclei and the cytoplasms, and further found that the N-terminal region of FHY1 is responsible for the interaction with FIN219. In subcellular localization studies, FIN219-YFP displayed different patterns in the fhy1-T protoplasts compared with that in wildtype, whereas FHY1-CFP was localized with the same patterns in the protoplasts of different mutant or transgenic plants. Further expression studies revealed that FIN219 negatively regulated FHY1 transcripts and positively FHY1 protein in both darkness and FR; whereas, FHY1 slightly negatively regulated FIN219 protein, instead of FIN219 transcript levels in darkness and FR. Taken together, these data indicate that FIN219 and FHY1 interacted with each other and were positively involved in phyA-mediated photomorphogenesis in Arabidopsis.
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