Roles of the nuclear-encoded chloroplast SMR domain-containing PPR protein SVR7 in photosynthesis and oxidative stress tolerance in Arabidopsis

The mutations of the plastid SMR domaincontaining PPR protein SVR7 were previously reported to cause a specific reduction in the chloroplast ATP synthase levels. Here, we isolated a new mutant allele of SVR7, named svr7-4, in which T-DNA is inserted into the initiation codon of SVR7. The rosette leaves of svr7-4, especially in the juvenile stage, showed a pale green phenotype as a result of a reduction in the chlorophyll levels. The values of P700 and Fv/Fm indicated that the photosynthetic capacities of both PSI and PSII were damaged in svr7-4. Furthermore, we found that the svr7-4 accumulated more reactive oxygen species (ROS) and showed lower photo-oxidative stress tolerance by histochemical staining and hydrogen peroxide bleaching experiments, respectively. The leaves of svr7-4 also had increased anthocyanins accumulation compared to that of wild-type (WT) when floated on water under light. Finally, we found that the expression levels of four abiotic stress-responsive genes including ZAT10, AtAPX1, CAT1 and AtGPX2 were up-regulated in svr7-4. SVR7 was expressed ubiquitously during plant development. These results indicate that SVR7 is important for normal photosynthesis and photo-oxidative stress responses in chloroplasts.