近日，华中农业大学果蔬园艺作物种质创新与利用全国重点实验室、园艺林学学院、湖北洪山实验室刘继红教授团队在国际期刊The Plant Cell发表题为 “A SNP in the 4-Coumarate CoA ligase 1-likeα promoter induces juice sac granulation by promoting BR-mediated lignin synthesis in citrus”的研究论文，揭示了启动子SNP变异通过油菜素内酯（BR）信号通路激活木质素合成造成柑橘果实整个生育期汁胞粒化的分子机制，阐明了相关分子调控网络，为柑橘汁胞粒化防控与分子育种提供重要靶标基因与理论支撑。
“金玉其外，败絮其中”是古人对柑橘果实粒化现象的记载，粒化果实汁胞硬化脱水，汁水流失、风味劣变。据统计，我国每年因汁胞粒化造成巨大的柑橘产业损失。以往研究大多聚焦果实成熟后期与采后贮藏阶段发生的粒化现象，而针对幼果发育阶段起始的早发型粒化及其分子机制，此前未见报道。
该研究利用清见（Citrus unshiu Marc × C. sinensis Osbeck）×鄂柑1号（C. reticulata Blanc.）杂交后代中一份从果实发育早期即持续发生汁胞粒化的独特柑橘株系开展系统研究。生理测定表明，相较于正常果实，粒化果实汁胞细胞壁显著增厚，木质素与BR含量显著升高。进一步整合基因组重测序和多时期转录组联合分析，筛选得到木质素合成关键基因Ci4CL1?likeα。该基因编码4?香豆酸辅酶A连接酶，正向推动木质素生物合成。深入研究表明，正常和粒化株系Ci4CL1?likeα 基因启动子上存在一个关键A/T单核苷酸多态性（SNP）变异，这一突变使CiMYB306可以特异性结合粒化类型果实的Ci4CL1-likeα启动子，激活Ci4CL1?likeα的表达，促进木质素合成。
研究团队进一步解析Ci4CL1-likeα上游调控模块，鉴定得到直接结合并激活CiMYB306的NAC家族转录因子CiNAC9。CiNAC9还能够直接靶向前激活Ci4CL1?likeα启动子。更重要的是，油菜素内酯BR能够显著增强CiNAC9的结合与转录激活能力，放大整个转录级联信号。综上所述，该研究阐明BR信号整合CiNAC9‑CiMYB306‑Ci4CL1‑likeα(A/T)分子模块木质素合成的分子机制和作用模块，解析了早发型柑橘粒化的遗传基础，为柑橘抗粒化育种及防控提供了理论依据和重要靶标基因。
华中农业大学园艺林学学院博士后楚乐乐为论文第一作者，刘继红教授为论文通讯作者。该研究得到国家自然科学基金（重点项目、青年C类）、中国博士后科学基金（面上、特别资助）、国家资助博士后研究人员计划和湖北省博士后尖端人才引进项目的资助。
论文链接：https://doi.org/10.1093/plcell/koag276
英文摘要：
Juice sac granulation （also known as 'Kushui‘）， characterized by hardening and dehydration, is a widespread physiological disorder that severely compromises fruit quality. However, the molecular mechanism and signaling pathways underlying this disorder remain largely unexplored. In this study, we identified a unique hybrid from a cross between Kiyomi （Citrus unshiu Marc × C. sinensis Osbeck） and Egan No. 1 tangerine （C. reticulata Blanc.） that exhibits the juice sac granulation from the onset of fruit development. Compared to normal fruits, 'Kushui' fruit （KS） exhibited significantly elevated levels of lignin and brassinolide （BR）。 Through resequencing and transcriptome analyses, we identified 4-Coumarate CoA ligase 1-likeα （Ci4CL1-likeα） as a key gene involved in lignin biosynthesis. Notably, a single nucleotide polymorphism （SNP, A/T） in the promoter region of Ci4CL1-likeα between KS （carrying T） and normal （carrying A） allowed the former to be successfully targeted and positively regulated by CiMYB306. In addition, both CiMYB306 and Ci4CL1-likeα were positively regulated by CiNAC9 through interacting with the NARC motifs in a BR-inducible way. Genetic evidences confirmed that CiMYB306 and CiNAC9 regulated lignin biosynthesis in a Ci4CL1-likeα-dependent manner. Taken together, our findings reveal that the mutation of A into T in the promoter of Ci4CL1-likeα creates a binding site recognized and positively activated by CiMYB306, which acts in synergy with CiNAC9 in a BR-responsive way, leading to enhanced lignin synthesis and fruit granulation. These findings gain valuable insight into the BR-mediated transcriptional regulatory module involved in fruit granulation and unravel potential targets for mitigating this disorder.
日期：2026-10-03
