Expression Analysis Reveals That Sorghum Disease Resistance Protein SbSGT1 Is Regulated by Auxin

SIMPLE SUMMARY: SGT1 (suppressor of the skp1 G2 allele, a component of the ubiquitin ligase complex), which is an important plant disease resistance-related protein, acts as a regulatory factor for signal transduction during the process of plant disease resistance, and is an important regulatory factor of defense response signals. Plant immunity is mediated by hormones, such as auxin; however, the molecular relationship between auxin and SGT1 remains unclear. In this study, we determined the expression patterns of SbSGT1 under different plant hormone treatments and the result showed that SbSGT1 was significantly upregulated. Thus, we examined the molecular interaction of SbSGT1 and indole-3-acetic acid in vitro and in vivo. The results will provide a reference for further investigation of the mechanisms underlying SbSGT1 involvement in the auxin signal transduction pathway. ABSTRACT: SGT1 (suppressor of the skp1 G2 allele) is an important plant disease resistance-related protein, which plays an important role in plant resistance to pathogens and regulates signal transduction during the process of plant disease resistance. In this study, we analyzed the expression profile of SbSGT1 in sorghum under phytohormones treatment. Quantitative real-time PCR results showed that SbSGT1 was most expressed in sorghum leaves, and could respond to plant hormones such as auxin, abscisic acid, salicylic acid, and brassinolide. Subsequently, we determined the optimal soluble prokaryotic expression conditions for SbSGT1 and purified it using a protein purification system in order to evaluate its potential interactions with plant hormones. Microscale thermophoretic analysis showed that SbSGT1 exhibited significant interactions with indole-3-acetic acid (IAA), with a Kd value of 1.5934. Furthermore, the transient expression of SbSGT1 in Nicotiana benthamiana indicated that treatment with exogenous auxin could inhibit SbSGT1 expression, both at the transcriptional and translational level, demonstrating that there exists an interaction between SbSGT1 and auxin.