Abscisic acid (ABA) is a critical regulator of seed development and germination. β-glucosidases (BGs) have been suggested to be contributors to increased ABA content because they catalyze the hydrolysis of ABA-glucose ester to release free ABA. However, whether BGs are involved in seed development is unclear. In this study, a candidate gene, ClBG1, in watermelon was selected for targeted mutagenesis via the CRISPR/Cas9 system. Seed size and weight were significantly reduced in the Clbg1-mutant watermelon lines, which was mainly attributed to decreased cell number resulting from decreased ABA levels. A transcriptome analysis showed that the expression of 1015 and 1429 unique genes was changed 10 and 18 days after pollination (DAP), respectively. Cytoskeleton- and cell cycle-related genes were enriched in the differentially expressed genes of wild type and Clbg1-mutant lines during seed development. Moreover, the expression of genes in the major signaling pathways of seed size control was also changed. In addition, seed germination was promoted in the Clbg1-mutant lines due to decreased ABA content. These results indicate that ClBG1 may be critical for watermelon seed size regulation and germination mainly through the modulation of ABA content and thereby the transcriptional regulation of cytoskeleton-, cell cycle- and signaling-related genes. Our results lay a foundation for dissecting the molecular mechanisms of controlling watermelon seed size, a key agricultural trait of significant economic importance.

中文翻译：

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CRISPR/Cas9 介导的 ClBG1 诱变减小了西瓜的种子大小并促进了种子萌发

脱落酸 (ABA) 是种子发育和发芽的关键调节剂。β-葡萄糖苷酶 (BG) 被认为是增加 ABA 含量的原因，因为它们催化 ABA-葡萄糖酯水解以释放游离 ABA。然而，BGs是否参与种子发育尚不清楚。在这项研究中，一个候选基因，CLBG1, 在西瓜中，通过 CRISPR/Cas9 系统选择进行靶向诱变。种子大小和重量显着减少Clbg1-突变西瓜系，这主要归因于ABA水平降低导致细胞数量减少。转录组分析表明，1015 和 1429 个独特基因的表达分别在授粉后 10 天和 18 天（DAP）发生了变化。细胞骨架和细胞周期相关基因在野生型和细胞周期的差异表达基因中富集。Clbg1-种子发育过程中的突变株系。此外，种子大小控制的主要信号通路中基因的表达也发生了变化。此外，促进种子发芽Clbg1-由于ABA含量降低而导致的突变系。这些结果表明CLBG1可能对西瓜种子大小调节和发芽至关重要，主要通过调节 ABA 含量，从而调节细胞骨架、细胞周期和信号传导相关基因的转录。我们的研究结果为剖析控制西瓜种子大小的分子机制奠定了基础，西瓜种子大小是具有重要经济意义的关键农业性状。