mutation induces bright yellow leaves by disrupting magnesium chelatase I subunit function in Chinese cabbage ( L. ssp. ).

Magnesium chelatase (MgCh) plays a pivotal role in photosynthesis, catalyzing the insertion of magnesium into protoporphyrin IX (Proto IX), a key intermediate in chlorophyll (Chl) biosynthesis. MgCh is a heteromeric complex composed of the MgCh D subunit (CHLD), the MgCh H subunit (CHLH), and the MgCh I subunit (CHLI). The () mutant was obtained through ethyl methanesulfonate (EMS) mutagenesis of the 'FT' Chinese cabbage ( L. ssp. ) doubled haploid line, whose Chl content, net photosynthetic rate (), and non-photochemical quenching coefficient (NPQ) were decreased, and whose chloroplast development was incomplete. recovered to a light green phenotype under weak light conditions. Genetic analysis revealed that the bright yellow leaves phenotype of was caused by a single recessive nuclear gene. Using Mutmap sequencing and Kompetitive allele-specific PCR (KASP) identification, , encoding the CHLI subunit of MgCh, was identified as the candidate gene and named A nonsynonymous G-to-A mutation in the exon resulted in the substitution of aspartic acid with asparagine. -silenced Chinese cabbage displayed bright yellow leaves with decreased expression. Transiently overexpressed in the mutant restored the green leaf phenotype and significantly increased relative expression levels. 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. Together, mutations impaired the function of MgCh, providing insights into the molecular mechanism of leaf coloration.