SlMAPK3 Enhances Tolerance to Salt Stress in Tomato plants by Scavenging ROS Accumulation and Up-regulating the Expression of Ethylene Signaling Related Genes

ABSTRACT Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction stimulus decoder that can translate extracellular signals into intracellular responses and play a crucial role in plant biotic and abiotic stress responses. However, no direct evidence of SlMAPK3 in response to salt stress of tomato plants had been obtained until now. Here, SlMAPK3 over-expression line (OE.MAPK3-5) and SlMAPK3 knock-out line (slmapk3-8) were used to investigate the role of SlMAPK3 in regulating tomato plants response to salt stress. The results showed that OE.MAPK3-5 plants showed higher fresh weight and seedlings height as well as seminal root length than wild type (WT) plants and slmapk3-8 plants under salt stress, which indicated that SlMAPK3 improved tomato tolerance to salt stress. In addition, knockout of SlMAPK3 increased salt sensitivity as revealed by the accumulation of H2O2 and MDA, reduction of soluble sugar and soluble protein contents, and suppression of antioxidant enzymes activities (POD, SOD, CAT and APX). High salinity induced cell death and chlorophyll degradation were more severe in slmapk3-8 plants but slighter in OE.MAPK3-5 plants compared with WT. Moreover, OE.MAPK3-5 plants exhibited increased expression of salt overly sensitive (SOS) pathway genes (SlSOS1, SlSOS2, SlSOS3) and ethylene signaling pathways genes (SlACS2, SlEIN2, SlERF2) compared with WT and slmapk3-8 plants under salt stress. These results unveil an expected function for SlMAPK3 in tomato plants positively response to salt stress by scavenging ROS accumulation and up-regulating the expression of ethylene signaling related genes.