Molecular Characterization of HSF Genes in Ricinus Communis L.: A Foundation for Breeding Stress-Resilient Genotypes

Abstract Ric inus com munis L., known as castor, is an industrial crop known for its globally high demand and valuable ricinoleic acid oil. It faces challenges as it is commonly cultivated globally under harsh environmental conditions in of arid/semi-arid regions. In Brazil, it is mainly cultivated by smallholder farmers in the northeastern semi-arid region, which has a relevant socioeconomic impact. Heat shock transcription factors (HSFs) represent an important class of heat shock protein (HSP) regulators in plants adapting to abiotic stress conditions. We characterized the RcHSF gene family expression under abiotic stress conditions in different tissues and stages of germination and seedling development, as the most critical phases for crop establishment and productivity. We identified 18 RcHSF genes (3 classes, 10 subclasses) distributed across 7 chromosomes containing cis-elements responsive to abiotic stresses (ABRE, MeJARE, GARE, SARE). Abiotic stresses (mannitol, saline, heat) did not affect total germination but compromised seedling vigor. RcHSFs responded to high and low temperatures during germination and early seedling. RcHSF08 (Class-A) was highly expressed under stresses in the early seedling stage, while RcHSF10 (Class-C) was induced during early seedling stages in control and all stresses compared to dry seeds. This study highlights RcHSF genes involved in abiotic stress tolerance across different Ricinus communis tissues during germination and early seedling growth, providing a foundation for future functional characterization of HSF genes in Arabidopsis thaliana and identifying promising candidates for R. communis breeding programs.