Abstract
The first step of chlorophyll biosynthesis is catalyzed by Mg-chelatase composed by subunits, CHLI, CHLD and CHLH. Mg-chelatase requires ATP hydrolysis attributed by CHLI. Arabidopsis possesses two CHLI isoforms, CHLI1 and CHLI2, showing similar expression profiles, but CHLI2 is suggested to have limited function on Mg-chelatase complex. Previously, we showed that Arabidopsis CHLI1 is active ATPase and a target of chloroplast thioredoxin (Trx). Here, we revealed that CHLI2 shows ATPase activity with lower Vmax and higher Km ATP values than those of CHLI1. We further confirmed Trx-dependent reduction of S-S bond of CHLI2 and thiol-modulation of ATPase activity. By crossing of homozygous CHLI1 (cs) and CHLI2 (CSHL_GT13937) mutants, we could select pale-green plants in F2 progenies, which segregated into three different types showing cs like pale-green, almost albino, and intermediate plants with ratio of 1:0.8:2. PCR analysis confirmed that CHLI2 mutation is semidominant, suggesting CHLI2 certainly functions in Mg-chelatase complex.
