BolMYB28-BolMAM1 Confers Salt and Drought Tolerance via Regulating Specific Aliphatic Glucosinolate Biosynthesis and Affecting ABA Accumulation in Broccoli.

Abstract

Glucosinolates (GSLs) are secondary metabolites popularly existing in Brassicaceae. However, the role and regulation of GSLs in environmental stress response remain ambiguous. Here, Methylthioalkylmalate synthase 1 (BolMAM1), a GSL biosynthesis-associated gene, was identified in broccoli. The overexpression of BolMAM1 enhanced both salt and drought tolerance in broccoli, along with an increase in aliphatic GSLs, such as 2(R)-hydroxy-3-butenyl GSL (progoitrin). Progoitrin could induce ABA accumulation in vitro. Consistently, ABA homoeostasis was modulated to accumulate more ABA in OEX-BolMAM1 transgenic broccoli. Moreover, sulforaphane (SFN), one of the hydrolysates of aliphatic GSLs, also exhibited accelerated accumulation in OEX-BolMAM1 transgenic broccoli. External application of SFN could rapidly induce stomatal closure. Furthermore, BolMYB28 was demonstrated to directly bind to the promoter of BolMAM1 and activate its transcription. These results indicated that BolMYB28-BolMAM1 confers tolerance to salt and drought stresses mainly by accelerating the biosynthesis of certain specific aliphatic GSLs. Progoitrin is a newly reported GSL positively regulating ABA accumulation. SFN may act as a signaling molecule to regulate stomatal behavior. These findings reveal the role of BolMYB28-BolMAM1 in abiotic stress response via regulating aliphatic GSL biosynthesis, and suggest the applications of progoitrin and SFN as natural defence factors to resist abiotic stresses in plants.