Genomic characterization and expression profiles of stress-associated proteins (SAPs) in castor bean (Ricinus communis)

Stress-associated proteins (SAPs) are known as response factors to multiple abiotic and biotic stresses in plants. However, the potential physiological and molecular functions of SAPs remain largely unclear. Castor bean (Ricinus communis L.) is one of the most economically valuable non-edible woody oilseed crops, able to be widely cultivated in marginal lands worldwide because of its broad adaptive capacity to soil and climate conditions. Whether SAPs in castor bean plays a key role in adapting diverse soil conditions and stresses remains unknown. In this study, we used the castor bean genome to identify and characterize nine castor bean SAP genes (RcSAP). Structural analysis showed that castor bean SAP gene structures and functional domain types vary greatly, differing in intron number, protein sequence, and functional domain type. Notably, the AN1-C2H2–C2H2 zinc finger domain within RcSAP9 has not been often observed in other plant families. High throughput RNA-seq data showed that castor bean SAP gene profiles varied among different tissues. In addition, castor bean SAP gene expression varied in response to different stresses, including salt, drought, heat, cold and ABA and MeJA, suggesting that the transcriptional regulation of castor bean SAP genes might operate independently of each other, and at least partially independent from ABA and MeJA signal pathways. Cis-element analyses for each castor bean SAP gene showed that no common cis-elements are shared across the nine castor bean SAP genes. Castor bean SAPs were localized to different regions of cells, including the cytoplasm, nucleus, and cytomembrane. This study provides a comprehensive profile of castor bean SAP genes that advances our understanding of their potential physiological and molecular functions in regulating growth and development and their responses to different abiotic stresses.