Wang Chaojie, Zhang Lili, Li Yingzhuang, Ali Buttar Zeeshan, Wang Na, Xie Yanzhou, Wang Chengshe
College of Agronomy, Northwest A&F University, Yangling, China.
State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling, China.
Front Plant Sci. 2020 Feb 20;11:97. doi: 10.3389/fpls.2020.00097. eCollection 2020.
Wheat ( L.) is one of the most important crops in the world. Chlorophyll plays a vital role in plant development and crop improvement and further determines the crop productivity to a certain extent. The biosynthesis of chlorophyll remains a complex metabolic process, and fundamental biochemical discoveries have resulted from studies of plant mutants with altered leaf color. In this study, we identified a chlorophyll-deficiency mutant, referred to as , from the wheat cultivar Shaannong33 that exhibited an obvious pale-green leaf phenotype at the seedling stage, with significantly decreased accumulation of chlorophyll and its precursors, protoporphyrin IX and Mg-protoporphyrin IX. Interestingly, a higher protoporphyrin IX to Mg-protoporphyrin IX ratio was observed in . Lipid biosynthesis in leaves and seeds was also affected, with the mutant displaying significantly reduced total lipid content relative to Shaanong33. Genetic analysis indicated that the pale-green leaf phenotype was controlled by a single pair of recessive nuclear genes. Furthermore, sequence alignment revealed a single-nucleotide mutation (G664A) in the gene TraesCS7A01G480700.1, which encodes subunit I of the Mg-chelatase in plants. This single-nucleotide mutation resulted in an amino acid substitution (D221N) in the highly conserved domain of subunit I. As a result, mutant protein Tachli-7A lost the ability to interact with the normal protein TaCHLI-7A, as assessed by yeast two-hybrid assay. Meanwhile, could not recover the chlorophyll deficiency phenotype of the SALK_050029 mutant. Furthermore, we found that in Shaannong33, the protoporphyrin IX to Mg-protoporphyrin IX ratio was growth state-dependent and insensitive to environmental change. Overall, the mutation in Tachli-7A impaired the function of Mg-chelatase and blocked the conversion of protoporphyrin IX to Mg- protoporphyrin IX. Based on our results, the mutant represents a potentially useful resource for better understanding chlorophyll and lipid biosynthetic pathways in common wheat.
小麦（L.）是世界上最重要的作物之一。叶绿素在植物发育和作物改良中起着至关重要的作用，并在一定程度上进一步决定作物生产力。叶绿素的生物合成仍然是一个复杂的代谢过程，对叶色改变的植物突变体的研究带来了重要的生化发现。在本研究中，我们从小麦品种陕农33中鉴定出一个叶绿素缺乏突变体，称为，该突变体在幼苗期表现出明显的淡绿叶表型，叶绿素及其前体原卟啉IX和镁原卟啉IX的积累显著减少。有趣的是，在中观察到原卟啉IX与镁原卟啉IX的比例更高。突变体叶片和种子中的脂质生物合成也受到影响，与陕农33相比，突变体的总脂质含量显著降低。遗传分析表明，淡绿叶表型由一对隐性核基因控制。此外，序列比对显示基因TraesCS7A01G480700.1中存在一个单核苷酸突变（G664A），该基因编码植物中镁螯合酶的亚基I。这个单核苷酸突变导致亚基I高度保守结构域中的一个氨基酸替换（D221N）。结果，通过酵母双杂交试验评估，突变蛋白Tachli - 7A失去了与正常蛋白TaCHLI - 7A相互作用的能力。同时，不能恢复SALK_050029突变体的叶绿素缺乏表型。此外，我们发现，在陕农33中，原卟啉IX与镁原卟啉IX的比例取决于生长状态，且对环境变化不敏感。总体而言，Tachli - 7A中的突变损害了镁螯合酶的功能，并阻断了原卟啉IX向镁原卟啉IX的转化。基于我们的结果，突变体是深入了解普通小麦叶绿素和脂质生物合成途径的潜在有用资源。
