Identification of the Functional Modules of SlPP2C.D—SlSAUR and Their Roles in Abscisic Acid-Mediated Inhibition of Tomato Hypocotyl Elongation

Abstract

The plant hormone ABA regulates various physiological processes, such as promoting stomatal closure and inhibiting hypocotyl elongation by mediating de-phosphorylation of H+-ATPase. However, the mechanism acting on ABA-induced de-phosphorylation of H+-ATPase remains largely unknown. SMALL AUXIN UP RNAs (SAURs), the largest family of early auxin-response genes, were well-reported to bind to and inhibit PP2C.D phosphatases to maintain plasma membrane H+-ATPase activity. In this study, we aimed to investigate whether SAUR-PP2C.D functional modules were involved in ABA-mediated inhibition of hypocotyl elongation. Here, we show that ABA suppresses hypocotyl elongation in both light-grown and dark-grown tomato seedlings in a dose-dependent manner. Hypocotyl elongation of dark-grown seedlings was more sensitive to ABA compared to that of light-grown seedlings. ABA upregulates seven SlPP2C.D genes. SlPP2C.D1 was highly expressed in hypocotyl and upregulated by light. Y2H data showed SlPP2C.D1 interacted with SlSAUR2, 35, 40, 55, 57, 59, 65, and 70. The other four SlPP2C.Ds were also associated with a subset of SAUR proteins. Our findings have provided new insights for further examination on the SAUR-PP2C.D modules that regulate outputs of ABA and other phytohormones controlling plant growth and development.