AUTHOR=Liu Chuanhong , Chai Yi , Tan Chong , Shi Fengyan , Zhang Yun , Liu Zhiyong 

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

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1450242

DOI=10.3389/fpls.2024.1450242

ISSN=1664-462X

ABSTRACT=<p>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 <italic>bright yellow leaves</italic> (<italic>byl</italic>) mutant was obtained through ethyl methanesulfonate (EMS) mutagenesis of the ‘FT’ Chinese cabbage (<italic>Brassica rapa</italic> L. ssp. <italic>pekinensis</italic>) doubled haploid line, whose Chl content, net photosynthetic rate (<italic>Pn</italic>), and non-photochemical quenching coefficient (NPQ) were decreased, and whose chloroplast development was incomplete. <italic>byl</italic> recovered to a light green phenotype under weak light conditions. Genetic analysis revealed that the bright yellow leaves phenotype of <italic>byl</italic> was caused by a single recessive nuclear gene. Using Mutmap sequencing and Kompetitive allele-specific PCR (KASP) identification, <italic>BraA01g010040.3.5C</italic>, encoding the CHLI subunit of MgCh, was identified as the candidate gene and named <italic>Brchli1.</italic> A nonsynonymous G-to-A mutation in the <italic>Brchli1</italic> exon resulted in the substitution of aspartic acid with asparagine. <italic>Brchli1</italic>-silenced Chinese cabbage displayed bright yellow leaves with decreased <italic>Brchli1</italic> expression. Transiently overexpressed <italic>Brchli1</italic> in the <italic>byl</italic> mutant restored the green leaf phenotype and significantly increased relative <italic>Brchli1</italic> 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, <italic>Brchli1</italic> mutations impaired the function of MgCh, providing insights into the molecular mechanism of leaf coloration.</p>