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The receptor-like kinase (RLK) family of receptors and the associated receptor-like cytoplasmic kinases (RLCKs) have expanded in plants because of selective pressure from environmental stress and evolving pathogens. RLCKs link pathogen perception to activation of coping mechanisms. RLK–RLCK modules regulate hormone synthesis and responses, reactive oxygen species (ROS) production, Ca2+ signaling, activation of mitogen-activated protein kinase (MAPK), and immune gene expression, all of which contribute to immunity. Some RLCKs integrate responses from multiple receptors recognizing distinct ligands. RLKs/RLCKs and nucleotide-binding domain, leucine-rich repeats (NLRs) were found to synergize, demonstrating the intertwined genetic network in plant immunity. Studies in arabidopsis (Arabidopsis thaliana) have provided paradigms about RLCK functions, but a lack of understanding of crop RLCKs undermines their application. In this review, we summarize current understanding of the diverse functions of RLCKs, based on model systems and observations in crop species, and the emerging role of RLCKs in pathogen and abiotic stress response signaling. 

SUMMARY Sorghum anthracnose caused by the fungusColletotrichum sublineola(Cs) is a damaging disease of the crop. Here, we describe the identification ofANTHRACNOSE RESISTANCE GENES(ARG4andARG5) encoding canonical nucleotide‐binding leucine‐rich repeat (NLR) receptors.ARG4andARG5are dominant resistance genes identified in the sorghum lines SAP135 and P9830, respectively, that show broad‐spectrum resistance toCs. Independent genetic studies using populations generated by crossing SAP135 and P9830 with TAM428, fine mapping using molecular markers, comparative genomics and gene expression studies determined thatARG4andARG5are resistance genes againstCsstrains. Interestingly,ARG4andARG5are both located within clusters of duplicate NLR genes at linked loci separated by ~1 Mb genomic region. SAP135 and P9830 each carry only one of theARGgenes while having the recessive allele at the second locus. Only two copies of theARG5candidate genes were present in the resistant P9830 line while five non‐functional copies were identified in the susceptible line. The resistant parents and their recombinant inbred lines carrying eitherARG4orARG5are resistant to strains Csgl1 and Csgrg suggesting that these genes have overlapping specificities. The role ofARG4andARG5in resistance was validated through sorghum lines carrying independent recessive alleles that show increased susceptibility.ARG4andARG5are located within complex loci displaying interesting haplotype structures and copy number variation that may have resulted from duplication. Overall, the identification of anthracnose resistance genes with unique haplotype stucture provides a foundation for genetic studies and resistance breeding.