Brchli1 mutation induces golden leaves by disrupting magnesium chelatase I subunit function in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

The chli1 golden leaf mutant was obtained through ethyl methanesulfonate (EMS) mutagenesis of the FT Chinese cabbage doubled haploid line, whose Chl content, net photosynthetic rate (Pn), and non-photochemical quenching coefficient (NPQ) were decreased, and whose chloroplast development was incomplete. chli1 recovered to a light green phenotype under weak light conditions. Genetic analysis revealed that the golden leaf phenotype of chli1 was caused by a single recessive nuclear gene. The candidate gene Brchli1 (BraA01g010040.3.5C), identified through MutMap sequencing and Kompetitive Allele-Specific PCR (KASP), harbored a point mutation at nucleotide 783. Brchli1-silenced Chinese cabbage displayed golden leaves with decreased Brchli1 expression. Both BrCHLI1 and its mutated variant were localized in chloroplasts. Yeast two-hybrid and luciferase complementation imaging assays demonstrated that BrCHLI1 interacted with both BrCHLD and itself. BrCHLI1 mutations did not affect its interaction with BrCHLD, but impaired its interaction with itself, resulting in decreased MgCh and ATPase activities.