Chlorophyll biosynthesis and chloroplast development are crucial to photosynthesis and plant growth, but their regulatory mechanism remains elusive in many crop species. We isolated a Brassica napus yellow-virescent leaf (yvl) mutant, which exhibited yellow-younger-leaf and virescent-older-leaf with decreased chlorophyll accumulation and delayed chloroplast development. We mapped yvl locus to a 70-kb interval between molecular markers yvl-O10 and InDel-O6 on chromosome A03 in BC₂F₂ population using whole genome re-sequencing and bulked segregant analysis. The mutant had a ‘C’ to ‘T’ substitution in the coding sequence of BnaA03.CHLH, which encodes putative H subunit of Mg-protoporphyrin IX chelatase (CHLH). The mutation resulted in an imperfect protein structure and reduced activity of CHLH. It also hampered the plastid encoded RNA polymerase which transcribes regulatory genes of photosystem II and I. Consequently, the chlorophyll a/b and carotenoid contents were reduced and the chloroplast ultrastructure was degraded in yvl mutant. These results explain that a single nucleotide mutation in BnaA03.CHLH impairs PEP activity to disrupt chloroplast development and chlorophyll biosynthesis in B. napus.

叶绿素的生物合成和叶绿体的发育对于光合作用和植物的生长至关重要，但是它们的调控机制在许多农作物中仍然难以捉摸。我们分离了甘蓝型油菜黄绿色叶（yvl）突变体，该突变体表现出黄幼叶和绿叶老叶，叶绿素积累减少，叶绿体发育延迟。我们使用全基因组重测序和大量分离子分析，将yvl基因座映射到BC ₂ F ₂群体中A03染色体上分子标记yvl-O10和InDel-O6之间的70-kb区间。该突变体在BnaA03.CHLH的编码序列中具有'C'到'T'取代，它编码Mg-原卟啉IX螯合酶（CHLH）的假定H亚基。突变导致蛋白质结构不完善，降低了CHLH的活性。它也阻碍了质体编码的RNA聚合酶的转录，后者转录了光系统II和I的调控基因。因此，yvl突变体中的叶绿素a / b和类胡萝卜素含量降低，叶绿体超微结构退化。这些结果说明，BnaA03.CHLH中的一个核苷酸突变会损害PEP活性，破坏甘蓝型油菜的叶绿体发育和叶绿素生物合成。