Cotton miR393-TIR1 Module Regulates Plant Defense Against via Auxin Perception and Signaling.

Plant auxin is essential in plant growth and development. However, the molecular mechanisms of auxin involvement in plant immunity are unclear. Here, we addressed the function of the cotton () miR393-TIR1 module in plant defense against infection via auxin perception and signaling. was directedly cleaved by ghr-miR393 according to mRNA degradome data, 5'-RACE analysis, and a GUS reporter assay. Ghr-miR393 knockdown significantly increased plant susceptibility to compared to the control, while ghr-miR393 overexpression and knockdown significantly increased plant resistance. External indole-3-acetic acid (IAA) application significantly enhanced susceptibility to in ghr-miR393 knockdown and control plants compared to mock treatment, and only slightly increased susceptibility in overexpressing ghr-miR393 and GhTIR1-silenced plants. Application of external PEO-IAA (an auxin antagonist) had a contrary trend with IAA application. Based on yeast two-hybrid and bimolecular fluorescence complementation assays, GhTIR1 interacted with GhIAA14 in the nucleus, and knockdown reduced plant resistance to infection. The results suggested that the ghr-miR393-GhTIR1 module regulates plant defense via auxin perception and signaling. Additionally, simultaneous knockdown of and significantly increased plant susceptibility to compared to the control, indicating that salicylic acid (SA) accumulation is vital for the ghr-miR393-GhTIR1 module to regulates plant resistance. Transcriptome data also demonstrated that knockdown significantly downregulated expression of auxin-related genes and upregulated expression of SA-related genes. Overall, the ghr-miR393-GhTIR1 module participates in plant response to infection via IAA perception and signaling partially depending on the SA defense pathway.