转录因子LcKNOX23调控荔枝落果的分子机制研究

As a native fruit crop of Southern China, litchi is very important in fruit research and industry, however, litchi is very vulnerable to fruit abscission before harvest, thus results in huge economic losses, so it is noteworthy to mine the key regulators controlling fruit abscission and their molecular mechanism. Currently, our previous RNA-seq analysis revealed that LcKNOX23, which belongs to the KNOX superfamily thranscriptional factor, may involve in fruit abscission. what’s important is that previous report have shown that KNOX transcriptional factors play key roles in regulating organ shedding, while the potential molecular mechanism is unclear. In this present project, to reveal the function and molecular mechanism of LcKNOX23 in controlling the fruit abscission, firstly, molecular characterization and transgenetic Arabidopsis analysis will be used to determine the key role of LcKNOX23 in regulating organ abscision, then, the function of LcKNOX23 in regulating organ shedding will be further determined by ectopic overexpression of LcKNOX23 in tomato, finally, to systematically elucidate the molecular mechanism of LcKNOX23 in controlling litchi fruit abscission, the targets of LcKNOX23 involved in fruit abscission progress will be isolated by ChIP-seq. The results obtained in this project will not only expand the mechanism controlling plant organ abscission, but also provide new essential theoretical support for improving cultivation management and cultivars.

荔枝是我国原产且研究和产业优势明显的南方果树，但其采前大量落果造成极大经济损失，因此挖掘调控荔枝落果的关键因子及探究其分子机制值得关注。本项目利用前期的RNA-seq初步筛选到一个可能与荔枝落果相关的KNOX转录因子LcKNOX23，而前人的研究表明KNOX转录因子在器官脱落中起重要作用，但其调控机理不清楚。本项目将以荔枝为材料，分析LcKNOX23转录因子的特征，结合异源转基因拟南芥器官脱落表型，初步确定LcKNOX23是调控荔枝落果的一个关键因子；进一步通过异源转基因番茄和ChIP-seq深入分析LcKNOX23转录因子的功能及其调控的靶基因，以期系统阐明LcKNOX23调控荔枝落果的分子机制。项目研究结果将丰富植物器官脱落调控的机制，并将为生产上改进荔枝落果管理措施及后期的分子改良提供新的重要理论基础。

荔枝起源于我国，是我国最具特色 和优势的南方水果之一，但其果实在生长发育过程中恰值南方梅雨季节，阴雨天气或其它逆境条件会导致荔枝果实大量脱落，这是造成我国荔枝产量低(全 国亩产不足200公斤)的一个重要原因。目前。关于调控荔枝落果的关键基因还未知。本研究发现一个KNOX类转录因子LcKNOX23在荔枝果柄离区的转录量远远多于近轴端和远轴端；此外，由LcKNOX23启动子驱动的GUS信号特异性的在拟南芥花器官离区和番茄花柄离区聚集，进一步证实LcKNOX23在离区特异性表达。qRT-PCR分析表明，荔枝落果过程中，LcKNOX23的转录量被显著性下调，说明LcKNOX23与荔枝落果负相关;此外qRT-PCR分析发现LcACS1/7和LcACO2/3与荔枝幼果脱落前的乙烯释放最相关;EMSA和荧光素酶双系统证实LcKNOX23可直接结合LcACS1/7和LcACO2/3并抑制其转录活性;转基因分析发现LcKNOX23完全抑制了拟南芥花器官的脱落和推迟了番茄花的脱落进程;最后，本研究发现24种(包括荔枝)具有代表性的陆生植物，从低等藻类植物到高等单双子叶植物，这些物种的ACS/ACO基因的启动子都包含KNOX转录因子的结合位点，说明KNOX转录因子调控乙烯合成在陆生植物中可能具有保守性，这将极大的扩展KNOX转录因子在植物中的功能。

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