ZmWGSL2 Is a Candidate Chloroplast-Localized PPR Gene Associated with Chloroplast Development and Leaf-Colour Formation in Maize

Abstract

Efficient chloroplast development underpins photosynthetic efficiency, biomass accumulation, and ultimately crop productivity. In this study, we characterized wgsl2-0, a stable white-green striped leaf mutant isolated from an ethyl methanesulfonate-mutagenized RP125 population of maize (Zea mays L.). The mutant maintained clear longitudinal striping throughout development and displayed lower chlorophyll content, reduced levels of several chlorophyll precursors and carotenoids, and reduced net photosynthetic rate in the green mutant sectors measured relative to WT. Cytological and ultrastructural analyses showed that the white sectors contained poorly differentiated chloroplasts with disorganized thylakoid membranes and abnormal leaf cellular architecture. Genetic analysis supported control by a single recessive nuclear locus. Fine mapping delimited the locus to an approximately 3.04 Mb interval on chromosome 1 between InDel-14 and InDel-26 and identified Zm00001eb043060, designated ZmWGSL2, as the most likely candidate gene. An independent nonsense allele, wgsl2-1, failed to complement wgsl2-0, strengthening the genetic evidence. ZmWGSL2 is a chloroplast-localized P-type PPR protein lacking recognizable E, E+, or DYW extensions. Representative Sanger chromatograms revealed altered rpoB nucleotide peak patterns in wgsl2-0, but these qualitative observations do not establish direct regulation of rpoB RNA editing by ZmWGSL2. Sector-specific reductions in several photosynthesis-associated plastid transcripts were observed in the white leaf sectors. Together, these results provide strong genetic evidence for ZmWGSL2 as the most likely candidate gene associated with chloroplast development and leaf-colour formation in maize.