Abscission is triggered by multiple environmental and developmental cues, including endogenous plant hormones. KNOTTED-LIKE HOMEOBOX (KNOX) transcription factors (TFs) play an important role in controlling abscission in plants. However, the underlying molecular mechanism of KNOX TFs in abscission is largely unknown. Here, we identified LcKNAT1, a KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1)-like protein from litchi, which regulates abscission by modulating ethylene biosynthesis. LcKNAT1 is expressed in the fruit abscission zone and its expression decreases during fruitlet abscission. Furthermore, the expression of the ethylene biosynthetic genes LcACS1, LcACS7, and LcACO2 increases in the fruit abscission zone, in parallel with the emission of ethylene in fruitlets. In vitro and in vivo assays revealed that LcKNAT1 inhibits the expression of LcACS/ACO genes by directly binding to their promoters. Moreover, ectopic expression of LcKNAT1 represses flower abscission in tomatoes. Transgenic plants expressing LcKNAT1 also showed consistently decreased expression of ACS/ACO genes. Collectively, these results indicate that LcKNAT1 represses abscission via the negative regulation of ethylene biosynthesis.

中文翻译：

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KNOX蛋白KNAT1通过抑制乙烯生物合成基因来调节荔枝中的小果脱落。

脱落是由多种环境和发育线索触发的，包括内源性植物激素。类似于KNOTTED的HOMEOBOX（KNOX）转录因子（TF）在控制植物的脱落中起重要作用。但是，KNOX TFs脱落的潜在分子机制在很大程度上尚不清楚。在这里，我们鉴定了LcKNAT1，一种来自荔枝的类似拟南芥THALIANA1（KNAT1）的蛋白，它通过调节乙烯的生物合成来调节脱落。LcKNAT1在果实脱落区表达，在果实脱落过程中表达降低。此外，乙烯生物合成基因LcACS1，LcACS7和LcACO2的表达果实脱落区中的乙烯含量增加，与果实中乙烯的释放量平行。体外和体内试验表明，LcKNAT1通过直接结合LcACS / ACO启动子来抑制其表达。此外，LcKNAT1的异位表达抑制了番茄中的花朵脱落。表达LcKNAT1的转基因植物还显示出ACS / ACO基因的表达持续下降。总的来说，这些结果表明LcKNAT1通过乙烯生物合成的负调控抑制脱落。