Comprehensive Evaluation and Transcriptome Analysis of Drought Resistance in Castor Bean (Ricinus communis L.)

Castor bean (Ricinus communis L.) is an important industrial oil crop worldwide. In China, western Jilin Province represents a major production region for this species, where spring drought severely constrains its yield and quality.This study aimed to comprehensively evaluate drought resistance in castor bean and explore its underlying mechanisms. A total of 40 common castor bean germplasms in Jilin Province were used as materials. Seedling drought resistance was evaluated using 25% polyethylene glycol (PEG) simulated drought stress, and agronomic traits were assessed under natural drought field conditions. Based on these evaluations, eight drought-tolerant and eight drought-sensitive germplasms were selected. Physiological indices and transcriptome sequencing (RNA-seq) were performed on the drought-tolerant genotype Baibi 22 and the drought-sensitive genotype Nongxuan 1. The 40 germplasms were classified into three drought resistance categories: drought-tolerant (8), moderately drought-tolerant (24), and drought-sensitive (8). Under 25% PEG stress, chlorophyll content decreased continuously, while peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) activities were higher than in the control, and malondialdehyde (MDA) content showed a unimodal increase. RNA-seq was used to identify 94 consistently differentially expressed genes (uDEGs) between the two germplasms at 3 and 7 days after stress, which were enriched in calcium signaling, redox balance, antioxidant stress, and the proteolytic ubiquitination pathway. Quantitative real-time PCR (qRT-PCR) verification confirmed the reliability of the RNA-seq results. This study screened elite drought-tolerant castor bean germplasms and identified 17 key genes related to abiotic stress regulation, providing germplasm resources and a molecular basis for improving abiotic stress resistance in castor bean through gene editing or molecular breeding.