Identification of the small auxin up-regulated RNA in tomato and investigation of SlSAUR50 as a positive regulator of tomato resistance to Botrytis cinerea.

The indole-3-acetic acid (IAA) signaling pathway plays a critical role in plant growth, development, and stress responses. Botrytis cinerea is a major biotic stress factor affecting tomato production. However, the mechanism by which small auxin up-regulated RNA (SAUR) genes participate in the response of tomato plants to B. cinerea remains unclear. In this study, the high-quality tomato genome SL4.0 was used to conduct a comprehensive genome-wide identification of 114 SlSAUR genes. We performed an integrative analysis of phylogenetic relationships, gene structure, cis-acting elements, gene duplications, and stress- and hormone-responsive expression patterns. Among the SAUR genes, SlSAUR50 was identified as a promising candidate because of its significant response to both B. cinerea infection and IAA treatment. Subcellular localization analysis revealed that SlSAUR50 was ubiquitously localized in protoplasts. Functional characterization showed that SlSAUR50 knockout aggravated B. cinerea infection in tomato leaves, whereas its overexpression significantly mitigated infection. Further analysis demonstrated that SlSAUR50 enhanced resistance to B. cinerea by promoting reactive oxygen species scavenging. In summary, this study provides a comprehensive analysis of the SAUR gene family in tomato and offers a theoretical basis for understanding the roles of SlSAUR genes, particularly SlSAUR50, in tomato's defense against B. cinerea infection.