Identification and expression analysis of SBP-Box-like (SPL) gene family disclose their contribution to abiotic stress and flower budding in pigeon pea (Cajanus cajan)

The SPL gene family (for Squamosa Promoter-binding like Proteins) represents specific transcription factors that have significant roles in abiotic stress tolerance, development and the growth processes of different plants, including initiation of the leaf, branching and development of shoot and fruits. The SPL gene family has been studied in different plant species; however, its role is not yet fully explored in pigeon pea (Cajanus cajan). In the present study, 11 members of the CcSPL gene family were identified in C. cajan. The identified SPLs were classified into nine groups based on a phylogenetic analysis involving SPL protein sequences from C. cajan, Arabidopsis thaliana, Cicer arietinum, Glycine max, Phaseolus vulgaris, Vigna unguiculata and Arachis hypogaea. Further, the identification of gene structure, motif analysis, domain analysis and presence of cis-regulatory elements in the SPL family members were studied. Based on RNA-sequencing data, gene expression analysis was performed, revealing that CcSPL2.1, 3 and 13A were significantly upregulated for salt-tolerance and CcSPL14 and 15 were upregulated in a salt-susceptible cultivar. Real-time qPCR validation indicated that CcSPL3, 4, 6 and 13A were upregulated under salt stress conditions. Therefore, molecular docking was performed against the proteins of two highly expressed genes (CcSPL3 and CcSPL14) with three ligands: abscisic acid, gibberellic acid and indole-3-acetic acid. Afterward, their binding affinity was obtained and three-dimensional structures were predicted. In the future, our study may open avenues for harnessing CcSPL genes in pigeon pea for enhanced abiotic stress resistance and developmental traits.