Abstract
Thidiazuron (TDZ) is widely used as a defoliant to induce leaf abscission in cotton. However, the underlying molecular mechanism is still unclear. In this study, RNA-seq and enzyme-linked immunosorbent assays (ELISA) were performed to reveal the dynamic transcriptome profiling and the change of endogenous phytohormones upon TDZ treatment in leaf, petiole, and abscission zone (AZ). We found that TDZ induced the gene expression of ethylene biosynthesis and signal, and promoted ethylene accumulation earlier in leaf than that in AZ. While TDZ down-regulated indole-3-acetic acid (IAA) biosynthesis genes mainly in leaf and IAA signal and transport genes. Furthermore, the IAA content reduced more sharply in the leaf than that in AZ to change the auxin gradient for abscission. TDZ suppressed CTK biosynthesis genes and induced CTK metabolic genes to reduce the IPA accumulation for the reduction of ethylene sensitivity. Furthermore, TDZ regulated the gene expression of abscisic acid (ABA) biosynthesis and signal and induced ABA accumulation between 12–48 h, which could up-regulate ABA response factor genes and inhibit IAA transporter genes. Our data suggest that TDZ orchestrates metabolism and signal of ethylene, auxin, and cytokinin, and also the transport of auxin in leaf, petiole, and AZ, to control leaf abscission.
Highlights
Abscission, as an important biological process for plant survival and reproduction, is a highly coordinated event involving multiple changes in cell structure, metabolism, and gene expression [1]
The process of abscission has been proposed to comprise of four major steps including phase one, the cells differentiate into specialized cells namely abscission zone; phase two, acquisition of competence to respond to abscission signals; phase three, activation of abscission for organ shedding; phase four, sealing of the break by differentiation of a protective layer on the main body side of the AZ [3]
MITOGEN-ACTIVATED PROTEIN KINASE3/6 (MAPK3/6) is activated to inhibit the expression of the BREVIPEDICELLUS (BP)/KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1), triggering the downstream KNAT2/6 expression to promote the development of the abscission zones and initiate the shedding of the organs [8]
Summary
Abscission, as an important biological process for plant survival and reproduction, is a highly coordinated event involving multiple changes in cell structure, metabolism, and gene expression [1]. The process of abscission has been proposed to comprise of four major steps including phase one, the cells differentiate into specialized cells namely abscission zone; phase two, acquisition of competence to respond to abscission signals; phase three, activation of abscission for organ shedding; phase four, sealing of the break by differentiation of a protective layer on the main body side of the AZ [3]. MITOGEN-ACTIVATED PROTEIN KINASE3/6 (MAPK3/6) is activated to inhibit the expression of the BREVIPEDICELLUS (BP)/KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1), triggering the downstream KNAT2/6 expression to promote the development of the abscission zones and initiate the shedding of the organs [8]. The IDA-like gene was up-regulated during abscission but the up-regulation was not limited to AZ, while none of the soybean HAE-like genes identified show a transcript expression pattern specific to the AZ, it is proposed that the IDA-HAE/HSL2 signal transduction pathway is not critical to the abscission process in tomato and soybean plants [9]. The molecular regulatory mechanism of sensing endogenous and exogenous signals and initiating the whole process of abscission is still unclear
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