[대학원 생명과학과 세미나 안내]
연사 : 배현숙 교수(연세대학교 시스템생물학과)
연제 : Functions of CPP family chaperones in chloroplasts and the endomembrane system
일시 : 2018년 10월 5일 (금) 오후 5시
장소 : 하나과학관 A동 B131호
초청교수 : 김옥매 교수
Abstract
Angiosperms require light for chlorophyll biosynthesis because one reaction in the pathway, the reduction of protochlorophyllide (Pchlide) to chlorophyllide, is catalyzed by the light-dependent protochlorophyllide oxidoreductase (POR). We report that Chaperone-like Protein of POR 1 (CPP1), an essential protein for chloroplast development, plays a role in the regulation of POR stability and function. CPP1 contains a J-like domain and three transmembrane domains and is localized in the thylakoid and envelope membranes, and interacts with POR isoforms in chloroplasts. CPP1 can stabilize POR proteins with its “holdase” chaperone activity. CPP1 deficiency results in diminished POR protein accumulation and defective chlorophyll synthesis, leading to photobleaching and growth inhibition of plants under light conditions. CPP1 depletion also causes reduced POR accumulation in etioplasts of dark-grown plants and as a result impairs the formation of prolamellar bodies, which subsequently affects chloroplast biogenesis upon illumination. These findings and the ubiquitous presence of CPP1 in oxygenic photosynthetic organisms suggest the conserved nature of CPP1 function in the regulation of POR.
The Arabidopsis genome encodes two homologs of CPP1: CRS (Cdf-related gene Responsive to Senescence) and At3g51140, which was designated as CPP2. At the amino acid level, each has less than 50% sequence identity to CPP1. CRS function was previously reported by Cui et al. (2012). We next focused on CPP2. CPP2 has a J-like domain of DnaJ/Hsp40-type cochaperones, and four transmembrane domains. We observed that knockdown of CPP2 with RNAi in Arabidopsis results in de-etiolation in the dark and leaf yellowing in the light. Using genetic, biochemical, and transcriptomic analyses, we found that CPP2 is localized to both chloroplasts and the endomembrane system, and plays a dual role in plant development. In chloroplasts, CPP2 collaborates with CPP1 to promote chlorophyll biosynthesis by stabilizing POR enzymes with its holdase chaperone activity. In the endomembrane system, CPP2 enhanced BR signaling by interacting with and stabilizing BRI1. Thus, our data indicates that CPP1 represents a multifunctional enhancer of photomorphogenic developmental program in plants.