College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, China.
J Plant Physiol. 2012 Jan 1;169(1):78-85. doi: 10.1016/j.jplph.2011.08.005. Epub 2011 Sep 21.
The aim of this study was to obtain new insights into the mechanisms that regulate endogenous abscisic acid (ABA) levels by β-glucosidase genes during the development of watermelons (Citrullus lanatus) and under drought stress conditions. In total, five cDNAs from watermelons were cloned by using reverse transcription-PCR (RT-PCR). They included three cDNAs (ClBG1, ClBG2 and ClBG3) homologous to those that encode β-glucosidase l that hydrolyzes the ABA glucose ester (ABA-GE) to release active ABA, ClNCED4, which encodes 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme in ABA biosynthesis, and ClCYP707A1, encoding ABA 8'-hydroxylase. A BLAST homology search revealed that the sequences of cDNAs and the deduced amino acids of these genes showed a high degree of homology to comparable molecules of other plant species. During fruit development and ripening, the expressions of ClBG1, ClNCED4 and ClCYP707A1 were relatively low at an early stage, increased rapidly along with fruit ripening, and reached the highest levels at 27 days after full bloom (DAFB) at the harvest stage. This trend was consistent with the accumulation of ABA. The ClBG2 gene on the other hand was highly expressed at 5 DAFB, and then decreased gradually with fruit development. Unlike ClBG1 and ClBG2, the expression of ClBG3 was low at an early stage; its expression peak occurred at 15 DAFB and then declined to the lowest point. When watermelon seedlings were subjected to drought stress, expressions of ClBG1 and ClCYP707A1 were significantly down-regulated, while expressions of ClBG2 and ClNCED4 were up-regulated in the roots, stems and leaves. The expression of ClBG3 was down-regulated in root tissue, but was up-regulated in stems and leaves. In conclusion, endogenous ABA content was modulated by a dynamic balance between biosynthesis and catabolism regulated by ClNCED4, ClCYP707A1 and ClBGs during development and under drought stress condition. It seems likely that β-glucosidase genes are important for this regulation process.
本研究旨在通过β-葡萄糖苷酶基因获得有关内源脱落酸（ABA）水平调控机制的新见解，这些基因在西瓜（Citrullus lanatus）发育过程中和干旱胁迫条件下发挥作用。本研究共克隆了西瓜的 5 个 cDNA，它们包括 3 个 cDNA（ClBG1、ClBG2 和 ClBG3），这些 cDNA 与编码β-葡萄糖苷酶 l 的 cDNA 同源，该酶能水解 ABA 葡萄糖酯（ABA-GE）以释放具有活性的 ABA；ClNCED4 编码 9-顺式-环氧类胡萝卜素双加氧酶（NCED），这是 ABA 生物合成的关键酶；ClCYP707A1 编码 ABA 8'-羟化酶。BLAST 同源性搜索表明，这些基因的 cDNA 序列和推导的氨基酸与其他植物物种的可比分子具有高度同源性。在果实发育和成熟过程中，ClBG1、ClNCED4 和 ClCYP707A1 的表达在早期相对较低，随着果实成熟迅速增加，并在完全开花后 27 天（DAFB）达到收获期的最高水平。这一趋势与 ABA 的积累一致。另一方面，ClBG2 基因在 5 DAFB 时高度表达，然后随着果实发育逐渐减少。与 ClBG1 和 ClBG2 不同，ClBG3 的表达在早期较低；其表达峰值出现在 15 DAFB 时，然后下降到最低点。当西瓜幼苗受到干旱胁迫时，ClBG1 和 ClCYP707A1 的表达明显下调，而 ClBG2 和 ClNCED4 的表达在根、茎和叶中上调。ClBG3 的表达在根组织中下调，但在茎和叶中上调。总之，在发育过程中和干旱胁迫条件下，ClNCED4、ClCYP707A1 和 ClBGs 调节的生物合成和分解代谢的动态平衡调节了内源 ABA 含量。β-葡萄糖苷酶基因似乎对这一调节过程很重要。
