Institute of Industrial Crops, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China.
Key Laboratory of Cotton and Rapeseed, Ministry of Agriculture and Rural Affairs, Nanjing 210014, China.
Int J Mol Sci. 2022 Nov 17;23(22):14208. doi: 10.3390/ijms232214208.
Thidiazuron (TDZ) is the main defoliant used in production to promote leaf abscission for machine-picked cotton. Under low temperatures, the defoliation rate of cotton treated with TDZ decreases and the time of defoliation is delayed, but there is little information about this mechanism. In this study, RNA-seq and physiological analysis are performed to reveal the transcriptome profiling and change in endogenous phytohormones upon TDZ treatment in abscission zones (AZs) under different temperatures (daily mean temperatures: 25 °C and 15 °C). Genes differentially expressed in AZs between TDZ treatment and control under different temperatures were subjected to gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to compare the enriched GO terms and KEGG pathways between the two temperature conditions. The results show that, compared with the corresponding control group, TDZ induces many differentially expressed genes (DEGs) in AZs, and the results of the GO and KEGG analyses show that the plant hormone signaling transduction pathway is significantly regulated by TDZ. However, under low temperature, TDZ induced less DEGs, and the enriched GO terms and KEGG pathways were different with those under normal temperature condition. Many genes in the plant hormone signal transduction pathway could not be induced by TDZ under low temperature conditions. In particular, the upregulated ethylene-signaling genes and downregulated auxin-signaling genes in AZs treated with TDZ were significantly affected by low temperatures. Furthermore, the expression of ethylene and auxin synthesis genes and their content in AZs treated with TDZ were also regulated by low temperature conditions. The upregulated cell wall hydrolase genes induced by TDZ were inhibited by low temperatures. However, the inhibition of low temperature on genes in AZs treated with TDZ was relieved with the extension of the treatment time. Together, these results indicate that the responses of ethylene and auxin synthesis and the signaling pathway to TDZ are inhibited by low temperatures, which could not induce the expression of cell wall hydrolase genes, and then inhibit the separation of AZ cells and the abscission of cotton leaves. This result provides new insights into the mechanism of defoliation induced by TDZ under low temperature conditions.
噻苯隆（TDZ）是生产中主要的脱叶剂，用于促进机采棉的叶片脱落。在低温下，用 TDZ 处理的棉花脱叶率降低，脱叶时间延迟，但关于这种机制的信息很少。在这项研究中，通过 RNA-seq 和生理分析，揭示了在不同温度下（日平均温度：25°C 和 15°C）脱落区（AZ）中 TDZ 处理后内源植物激素的转录组谱和变化。对不同温度下 TDZ 处理和对照 AZ 中差异表达的基因进行基因本体（GO）和京都基因与基因组百科全书（KEGG）分析，比较两种温度条件下富集的 GO 术语和 KEGG 途径。结果表明，与相应的对照组相比，TDZ 在 AZ 中诱导了许多差异表达基因（DEGs），GO 和 KEGG 分析的结果表明，植物激素信号转导途径受到 TDZ 的显著调控。然而，在低温下，TDZ 诱导的 DEGs 较少，富集的 GO 术语和 KEGG 途径与正常温度条件下的不同。低温下，许多植物激素信号转导途径中的基因不能被 TDZ 诱导。特别是，TDZ 处理的 AZ 中上调的乙烯信号基因和下调的生长素信号基因受到低温的显著影响。此外，TDZ 处理的 AZ 中乙烯和生长素合成基因的表达及其含量也受到低温条件的调控。TDZ 诱导的细胞壁水解酶基因的上调受到低温的抑制。然而，随着处理时间的延长，低温对 TDZ 处理的 AZ 中基因的抑制作用得到缓解。总之，这些结果表明，乙烯和生长素合成及信号通路对 TDZ 的反应受到低温的抑制，不能诱导细胞壁水解酶基因的表达，从而抑制 AZ 细胞的分离和棉花叶片的脱落。这一结果为低温条件下 TDZ 诱导脱叶的机制提供了新的见解。
