Lemmon Schlessinger, 2010). A number of RLKs happen to be reported to become involved in

Lemmon Schlessinger, 2010). A number of RLKs have already been reported to be involved in ABA signaling pathways and stress tolerance in Arabidopsis (Osakabe et al., 2005; Bai et al., 2009; Deng et al., 2009; Xin et al., 2009; Osakabe et al., 2010; Hua et al., 2012; Tanaka et al., 2012; Yu et al., 2012). Mutation of receptorlike kinase 1 (RPK1) decreases ABA sensitivity during the approach of seed germination, seedling development, and stomatal movement, whereas RPK1 overproduction increases plant tolerance to dehydration and oxidative tension (Osakabe et al., 2005; Osakabe et al., 2010). Impairment of prolinerich extensin-like receptor kinase four (PERK4) reduces ABAinhibited root development by decreasing cytosolic cost-free calcium concentration and Ca2+ signaling (Bai et al., 2009). ABA INSENSITIVE3 (ABI3)-activated lectin receptor-like kinase LecRK-b2 positively regulates ABA signaling through seed germination, whereas the A4 subfamily of lectin receptor kinase members, LecRKA4.1, LecRKA4.2 and LecRKA4.3, play unfavorable and redundant roles in ABA responses (Deng et al., 2009; Xin et al., 2009). GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1) participates in ABAand H2O2-regulated activation of S-type anion currents in guard cells, which can be inhibited by ABI2 but not ABI1 (Hua et al., 2012). A positive regulator of auxin signaling, FERONIA (FER), interacts with guanine exchange elements GEF1, GEF4, and GEF10, which activate GTPase ROP11/ ARAC10 as well as the activated ROP11 enhances the ABI2 phosphatase activity (Yu et al.TROP-2 Protein Biological Activity , 2012). The RLK subfamily of cysteine-rich receptor-like protein kinases (CRKs) consists of 46 members in Arabidopsis, that are defined by two copies of DUF26 domains each of which include CX X motifs forming disulfide bonds for protein rotein interactions inside the extracellular area (Wrzaczek et al., 2010). Over-production of CRK5 or CRK13 enhances plant resistance to Pseudomonas syringae (Chen et al., 2003; Acharya et al., 2007). Induced expression from the four structurally closely connected CRKs, CRK4, CRK5, CRK19 and CRK20, results in hypersensitive response-associated cell death in transgenic Arabidopsis (Chen et al., 2003, 2004). CRK7 has been reported to become involved in mediating the responses to extracellular ROS production (Idanheimo et al., 2014). The signaling pathways mediated by many CRKs, including BR-insensitive 1 (BRI1) (Wang et al., 2001) and FLAGELLIN-SENSITIVE2 (FLS2) (Gomez-Gomez et al., 2001), have been effectively characterized in hormone perception and pathogen response. Two abiotic stress-inducible CRK members, CRK36 and a receptor-like cytosolic kinase (RLCK), ARCK1, interact with every other and negatively regulate ABA and osmotic anxiety signal transduction (Tanaka et al.IL-13, Mouse , 2012).PMID:24580853 Nevertheless, the function of many of the CRK members remains unknown. Within this study, we showed that overexpression of a membrane-localized cysteine-rich repeat RLK-encoding gene, CRK5, enhances plant sensitivity to ABA and improves drought resistance, whereas overexpression of a mutant form of CRK5, CRK5K372E, induces no significant ABA-related phenotypes. Transgenic lines of the two homologous genes of CRK5, CRK4 and CRK19, also exhibit ABA-hypersensitive phenotypes in early seedling growth. Overexpression of CRK4 also enhances ABA sensitivity of stomatal movement and drought tolerance. The expression of CRK5 is repressed by cooperation on the WRKY transcription factors WRKY18, WRKY40 and WRKY60. These data suggest that CRK5 is positively involved in ABA.