National Engineering Laboratory for Tree Breeding, College of Biological Sciences and Technology, Beijing Forestry University, Tsinghua East Road 35, Haidian District, Beijing 100083, PR China.
J Exp Bot. 2017 Apr 1;68(9):2361-2375. doi: 10.1093/jxb/erx097.
Desiccation tolerance (DT) is the crucial ability of seeds to resist desiccation. However, the regulatory mechanisms of seed DT are not fully understood. In this study, two heat shock cis-elements (HSEs) were identified in the Brassica napus galactinol synthase (BnGolS1) promoter and shown to bind the heat shock transcription factor A4a (BnHSFA4a). Transcriptional expression of BnHSFA4a was induced at the early stage of DT acquisition, prior to increased BnGolS1 activity and galactinol production. Ectopic overexpression of BnHSFA4a (oxBnHSFA4a) in Arabidopsis enhanced DT, particularly during DT re-establishment. OxBnHSFA4a up-regulated the expression of GolS1, GolS2, and raffinose synthase 2 (BnRS2) in Arabidopsis and increased the enzymatic activity of GolS and RS and the concentration of raffinose family oligosaccharides (RFOs). Additionally, the overexpression lines exhibited increased antioxidant abilities. In contrast, the Arabidopsis mutant athsfa4a was more sensitive to dehydration, showing decreases in the efficiency of DT re-establishment, RFO contents, and oxidation resistance. Complementation analysis indicated that DT was rescued in athsfa4a/BnHSFA4a seeds to similar levels compared with those of Col-0. Taken together, these results indicated that BnHSFA4a probably functions in the regulation of GolS expression and activity, and activation of the antioxidative system and other stress response factors to improve DT.
脱水耐性（DT）是种子抵抗干燥的关键能力。然而，种子 DT 的调控机制尚不完全清楚。在本研究中，在甘蓝型油菜半乳糖醇合酶（BnGolS1）启动子中鉴定出两个热休克顺式元件（HSEs），并证实其与热休克转录因子 A4a（BnHSFA4a）结合。BnHSFA4a 的转录表达在 DT 获得的早期阶段被诱导，早于 BnGolS1 活性和半乳糖醇产生的增加。拟南芥中 BnHSFA4a 的异位过表达（oxBnHSFA4a）增强了 DT，特别是在 DT 重建过程中。oxBnHSFA4a 在拟南芥中上调了 GolS1、GolS2 和 raffinose synthase 2（BnRS2）的表达，并增加了 GolS 和 RS 的酶活性以及 raffinose 家族寡糖（RFOs）的浓度。此外，过表达系表现出增强的抗氧化能力。相比之下，拟南芥突变体 athsfa4a 对脱水更敏感，DT 重建效率、RFO 含量和氧化抗性降低。互补分析表明，在 athsfa4a/BnHSFA4a 种子中，DT 得到了类似于 Col-0 的挽救。总之，这些结果表明 BnHSFA4a 可能在调节 GolS 的表达和活性、激活抗氧化系统和其他应激响应因子方面发挥作用，以提高 DT。
