A Receptor-Like Kinase That Functions in Adaptation to Salt Stress in Legumes

show that Srlk is rapidly induced by salt stress in M. truncatula roots, rather than in response to mannitol or cold temperature. Experiments with the Srlk-promoter fused to a b-glucuronidase marker gene showed that Srlk expression is strongly induced in root epidermal cells in response to salt. Repression of Srlk using RNA interference (RNAi) and mutations of Srlk introduced through TILLING prevented the inhibition of root growth under high salt conditions (see figure). In addition, Srlk mutant plants were found to accumulate significantly less sodium than control plants. Finally, several other salt-induced genes showed drastically reduced levels of induction following salt stress in the Srlk mutants relative to controls. RLKs possess an extracellular domain connected via a transmembrane domain to a cytoplasmic kinase. Plants contain hundreds of RLKs, which are thought to have overlapping or distinct roles in perceiving environmental and developmental signals and transducing these signals to downstream effectors (reviewed in Morillo and Tax, 2006). The results of de Lorenzo et al. suggest that Srlk may play a primary role in the perception of salt stress by M. truncatula roots and the ability of the plant to accumulate sodium under high salt conditions. Plant response to high salt and other stresses is highly complex, making genetic modification of plants for improved stress tolerance difficult to achieve (Wang et al., 2003). It will be important to identify downstream signaling partners and target genes of Srlk in the response and adaptation to salt stress. This work opens a new pathway for investigation and enhanced prospects for the development of improved salt tolerance in