Comparative transcriptome analysis of green/white variegated sectors in Arabidopsis yellow variegated2: Responses to oxidative and other stresses in white sectors

The yellow variegated2 (var2) mutant in Arabidopsis thaliana has been studied as a typical leaf-variegated mutant whose defect results from the lack of FtsH2 metalloprotease in chloroplasts. The var2 green sectors suffer from photo-oxidative stress and accumulate high levels of reactive oxygen species (ROS) because of compromised Photosystem II repair. This study investigated and compared microarray-based expression profiles of green and white sectors of var2 leaves. Results suggest that ROS that accumulate in chloroplasts of var2 green sectors do not cause much significant change in the transcriptional profile related to ROS signalling and scavenging. By contrast, transcriptome in the white sectors apparently differs from those in the green sectors and wild type. Numerous genes related to photosynthesis and chloroplast functions were repressed in the white sectors. Furthermore, many genes related to oxidative stress were up-regulated. Among them, ROS scavenging genes were specifically examined, such as Cu/Zn superoxide dismutase 2 (CSD2), that were apparently up-regulated in white but not in the green sectors. Up-regulation of CSD2 appears to be partly attributable to the lack of a microRNA (miR398) in the white sectors. It was concluded that the white sectors exhibit a response to oxidative and other stresses, including CSD2 up-regulation, which might be commonly found in tissues with abnormal chloroplast differentiation.