Studies on Protein Targeting to Thylakoids Using Maize csr1 Mutants

Abstract

At least 4 distinct protein targeting pathways to thylakoid membranes are known: 1) the Sec-dependent, 2) the signal recognition particle (SRP)-dependent, 3) the ΔpH-dependent, and 4) the spontaneous pathway. The SRP pathway, which is used for the insertion of light-harvesting chlorophyll proteins (LHCPs) involves cpSRP43, cpSRP54 and a SRP receptor cpFtsY. The objective of this work is to gain the insight into the roles of cpFtsY on the biogenesis of chloroplast. We have succeeded in isolating csr (chloroplast SRP receptor) 1-1 and 1-3 mutants which possess a Mu transposon insertion into the cpFtsY gene. Null cpFtsY mutant csr1-1, showed a pale green phenotype, whereas csr1-3 was a low expression line which had pale yellow green leaves. Both mutants were seedling lethal. csr1-1 chloroplasts exhibited severe pleiotropic defects in the architecture of the thylakoid membrane.