Shi Cong, Gu Miaofeng, Huang Yongjing, You Congjun, Bao Sihan, Xie Shuangling, Gong Jinli, Deng Guiming, Wu Pingzhi, Wu Wen, Zhu Congyi, Sun Xuepeng, Zeng Jiwu
Key Laboratory of Quality and Safety Control for Subtropical Fruit and Vegetable, Ministry of Agriculture and Rural Affairs, Zhejiang A&F University, Hangzhou, Zhejiang, 311300, China.
Institute of Fruit Tree Research, Key Laboratory of South Subtropical Fruit Biology and Genetic Resource Utilization (MOA), Guangdong Province Key Laboratory of Science and Technology Research on Fruit Tree Research, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, China.
BMC Plant Biol. 2025 Apr 15;25(1):472. doi: 10.1186/s12870-025-06496-9.
The 'Gonggan' mandarin, an elite local cultivar from Zhaoqing City, Guangdong Province, combines the qualities of mandarin and sweet orange. A leaf-variegated mutant enhances its ornamental and economic value, providing an excellent model for studying chloroplast development and photosynthetic pigment metabolism in citrus.
We found that, in this variegated mutant, chloroplasts are severely deficient or absent in mesophyll cells. Physiological assessments revealed lower levels of chlorophyll, carotenoids, net photosynthetic rate (Pn), and stomatal conductance (Gs), alongside significantly higher non-photochemical quenching (NPQ) and the non-photochemical quenching coefficient (qN), reflecting increased photoprotective energy dissipation. To uncover the molecular basis of leaf variegation, high-quality genome assemblies and transcriptomes were generated for both the normal and variegated 'Gonggan' mandarin, enabling comparative multi-omics analysis. Key genes involved in chloroplast development, such as TOC159, PDV2, THA8, and SIG5, were downregulated in the variegated leaves. Similarly, structural genes linked to chlorophyll degradation, including CLH2, SGR, NOL, and NYC1, exhibited altered expression. Downregulation of transcription factors GLK, GNC, and GNC-LIKE (GNL), known regulators of chloroplast development and chlorophyll biosynthesis, was also observed.
These findings suggest that disrupted expression of critical genes impacts chloroplast development and pigment metabolism, causing the leaf variegation phenotype. Overall, this study lays a foundation for functional genomics research and potential germplasm improvement of 'Gonggan' mandarin, and provides new insights into the mechanisms driving color variation in citrus.
“贡柑”是广东省肇庆市的优良地方品种，兼具柑和甜橙的品质。一种叶色斑驳的突变体提高了其观赏价值和经济价值，为研究柑橘叶绿体发育和光合色素代谢提供了一个优良模型。
我们发现，在这种斑驳突变体中，叶肉细胞中的叶绿体严重缺乏或缺失。生理评估显示，叶绿素、类胡萝卜素、净光合速率（Pn）和气孔导度（Gs）水平较低，同时非光化学猝灭（NPQ）和非光化学猝灭系数（qN）显著较高，这反映了光保护能量耗散增加。为了揭示叶片斑驳的分子基础，我们为正常和斑驳的“贡柑”生成了高质量的基因组组装和转录组，从而能够进行比较多组学分析。参与叶绿体发育的关键基因，如TOC159、PDV2、THA8和SIG5，在斑驳叶片中下调。同样，与叶绿素降解相关的结构基因，包括CLH2、SGR、NOL和NYC1，也表现出表达改变。还观察到转录因子GLK、GNC和类GNC（GNL）（已知的叶绿体发育和叶绿素生物合成调节因子）的下调。
这些发现表明，关键基因的表达紊乱影响叶绿体发育和色素代谢，导致叶片斑驳表型。总体而言，本研究为“贡柑”的功能基因组学研究和潜在种质改良奠定了基础，并为柑橘颜色变异的驱动机制提供了新的见解。
