Differential expression of oxygen-evolving polypeptide genes in maize leaf cell types

Abstract

Three polypeptides of 33 kD, 23 kD and 16 kD are released from maize photosystem II particles by alkaline Tris solution treatment and shown to cross-react with antisera to purified spinach oxygen-evolving (OE) polypeptides of 34 kD, 23 kD and 17 kD, respectively. They are not located exclusively in mesophyll cells but each is about 4 times more abundant in the thylakoid membranes of mesophyll than bundle sheath cells of etiolated, greening and green leaves. Three maize cDNA clones (OE33, OE23, OE16) have been identified by hybrid-selection, in vitro translation and immunoprecipitation with antisera against spinach OEs. Transcripts of all three genes are already detectable in both mesophyll and bundle sheath cells of etiolated leaves; however, they accumulate transiently and coordinately in mesophyll cells but remain at a constant low level in bundle sheath cells upon illumination of dark-grown maize seedlings. Moreover, the level of each protein increases in mesophyll cells following the accumulation of transcripts during greening and remains high in late greening and green leaves, despite the decline in each corresponding mRNA. The accumulation of all three OE proteins is also stimulated by light in bundle sheath cells without increases in their corresponding mRNAs. The preferential localization of these three proteins in mesophyll cells is due to both transcriptional and translational regulation.