[Genome-wide identification, expression profiling, and natural allelic variation analysis of the ckx genes in sorghum (Sorghum bicolor)].

Cytokinin (CK) is one of the essential plant hormones, and cytokinin oxidase (CKX) is the key enzyme for CK degradation. Currently, the ckx gene family of rice (Oryza sativa) and maize (Zea mays) have been characterized, while a genome-wide analysis of the ckx gene family in sorghum (Sorghum bicolor) has not been reported. This study aims to identify the Sbckx gene family in sorghum, analyze its evolutionary characteristics and expression patterns, and screen for key genes. A combined approach of bioinformatics analysis and experimental validation was utilized to examine sorghum subjected to abiotic stress conditions: low nitrogen and drought, as well as biotic stress induced by infections of head smut pathogens and sugarcane aphids, and the expression levels of Sbckxs were measured. A total of eleven Sbckxs were identified from the sorghum genome, exhibiting uneven distribution across chromosomes SBI-01, SBI-03,SBI-04, SBI-06, SBI-07, SBI-09, and SBI-010 (notably, chromosome SBI-03 contained four genes arranged in a clustered pattern). The SbCKX family proteins all contained the FAD-binding and cytokin-binding conserved domains. They exhibited high homology with the CKX family of five species including maize and rice and were classified into five evolutionary groups based on phylogenetic analysis. The expression pattern of SbCKXs exhibited tissue specificity. Specifically, Sbckx1-3g and Sbckx4-3g demonstrated high expression levels in roots and seedlings, whereas Sbckx11-7g was exclusively expressed in the panicle. Under conditions of drought, low nitrogen availability, and head smut infection, the expression levels of certain genes were notably elevated. The predicted interacting proteins of SbCKXs were implicated in pathways associated with growth, development, and substance metabolism. DNA variant analysis of re-sequenced sorghum germplasm revealed a high frequency of non-synonymous SNPs and INDELs in Sbckx10-10g across multiple cultivars. This study is the first to systematically analyze the molecular characteristics, expression patterns, and allelic variations of the ckx gene family in sorghum, providing a theoretical basis for subsequent functional verification of Sbckxs and molecular breeding for improving the stress resistance and yield of sorghum.