College of Forestry, Henan University of Science and Technology, Luoyang, China.
Key Laboratory of Tea Quality and Safety Control, Ministry of Agriculture, Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou, China.
Physiol Plant. 2021 Jun;172(2):885-895. doi: 10.1111/ppl.13243. Epub 2020 Nov 5.
The WRKY transcription factors (TFs) play multifaceted roles in plant growth, development, and stress response. Previously, we found that SlWRKY81 negatively regulates tomato tolerance to drought; however, the mechanisms of stomatal regulation in response to drought remain largely unclear. Here, we showed that drought-induced upregulation in the SlWRKY81 transcripts induced photoinhibition and reduced the net photosynthetic rate in tomato leaves. However, silencing SlWRKY81 alleviated those inhibitions and minimized the drought-induced damage. A time-course of water loss showed that SlWRKY81 silencing significantly and consistently reduced leaf water loss, suggesting a role for SlWRKY81 in stomatal movement. Further analysis using light microscopy revealed that SlWRKY81 silencing significantly decreased stomatal aperture and increased the ratio of length to width of stomata under drought. Both biochemical assay and confocal laser scanning microscopy demonstrated that drought-induced upregulation in SlWRKY81 expression inhibited the nitric oxide (NO) accumulation in the guard cells, which was attributed to the simultaneous declines in the activity of nitrate reductase (NR) and NR expression in tomato leaves. The inspection of 3-kb sequences upstream of the predicted transcriptional start site of the NR identified three copies of the core W-box (TTGACC/T) sequence in the promoter region, indicating possible targets of SlWRKY81. Taken together, these data suggest that SlWRKY81 potentially represses NR transcription and thus reduces NO accumulation to attenuate stomatal closure and subsequent drought tolerance. These findings provide an improved understanding of the mechanism of WRKY-induced regulation of stomatal closure, which can be exploited in the future to enhance drought tolerance in crops.
WRKY 转录因子（TFs）在植物生长、发育和应激响应中发挥着多方面的作用。此前，我们发现 SlWRKY81 负调控番茄对干旱的耐受性；然而，响应干旱调节气孔的机制在很大程度上仍不清楚。在这里，我们表明干旱诱导的 SlWRKY81 转录本上调诱导光抑制并降低番茄叶片的净光合速率。然而，沉默 SlWRKY81 缓解了这些抑制作用，并最大限度地减少了干旱引起的损伤。失水时间过程表明，沉默 SlWRKY81 显著且一致地降低了叶片水分损失，表明 SlWRKY81 在气孔运动中起作用。使用光显微镜进行的进一步分析表明，沉默 SlWRKY81 显著降低了干旱下气孔孔径，并增加了气孔长度与宽度的比值。生化测定和共聚焦激光扫描显微镜均表明，干旱诱导的 SlWRKY81 表达上调抑制了保卫细胞中一氧化氮（NO）的积累，这归因于番茄叶片中硝酸还原酶（NR）活性和 NR 表达的同时下降。在 NR 预测转录起始位点上游的 3kb 序列的检查中，在启动子区域发现了三个核心 W-box（TTGACC/T）序列的拷贝，表明 SlWRKY81 的可能靶标。总之，这些数据表明 SlWRKY81 可能抑制 NR 转录，从而减少 NO 积累以减轻气孔关闭和随后的耐旱性。这些发现提供了对 WRKY 诱导的气孔关闭调节机制的更好理解，可在未来用于提高作物的耐旱性。
