Preliminary Study On The Regulation Mechanism Of PHR2 In Chloroplast Development

Chloroplasts are important organs for photosynthesis in plants,and are the main sites for converting light energy into stable chemical energy.The normal development and exercise of chloroplasts directly affect the photosynthetic capacity and yield of plants.PHR2(Photolyase/Blue-Light Receptor 2)is a homologous protein of the CRY3(Cryptochrome 3).In this study,we discovered that two T-DNA insertion mutants,phr2-1 and phr2-2 of PHR2,had albino-lethal phenotypes.Ultrastructural analysis of chloroplasts revealed that the albino mutations were caused by abnormal development of chloroplasts.Through complement experiments,we demonstrated that CDS of PHR2 can restore the mutant phenotype.In addition,exogenous addition of 2%Sucrose can make the albino cotyledons turn pale green.After 60 days,the seedlings develop to seedlings,flowering but not pod formation,indicating that exogenous addition of sucrose can partially restore the albino phenotype of phr2.The PHR2 gene is expressed in the roots,hypocotyls,cotyledons,inflorescences of mature plants,and germinated embryos in Arabidopsis seedlings.Tissue-specific expression of PHR2 is regulated by light.With the increase of light time,the expression of PHR2 in cotyledons increases,while the expression of PHR2 decreases in the hypocotyl.In addition,during seed germination,the expression of PHR2 increased significantly during soaking,and exogenous application of ABA could inhibit PHR2 expression during this period.The subcell localization of PHR2 protein is the chloroplast.Preliminary research on the function of PHR2 in chloroplasts showed that PHR2 affects PEP-mediated transcription of chloroplast genes PsaB,PetD,PsbA,etc,but hardly affects the transcriptional activity of NEP,indicating that PHR2 may participate in the transcriptional regulation of chloroplast genes.Through in vitro experiments,we have initially demonstrated that PHR2 can interact with PIP1.Because PIP1 is localized in the nucleus and cytoplasm,we speculate that PIP1 may affect the folding,homeostasis,or localization of PHR2 protein through interaction with PHR2,thereby affecting chloroplast development.The above results indicate that PHR2 is an important member that affects the development of chloroplasts in Arabidopsis,and the study of this gene will lay a good foundation for further understanding the molecular mechanism of chloroplast development regulation.