Accurate Long-Read RNA Sequencing Analysis Reveals the Key Pathways and Candidate Genes under Drought Stress in the Seed Germination Stage in Faba Bean.

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Faba bean is an important pulse. It provides proteins for the human diet and is used in industrial foodstuffs, such as flours. Drought stress severely reduces the yield of faba bean, and this can be efficiently overcome through the identification and application of key genes in response to drought. In this study, PacBio and Illumina RNA sequencing techniques were used to identify the key pathways and candidate genes involved in drought stress response. During seed germination, a total of 17,927 full-length transcripts and 12,760 protein-coding genes were obtained. There were 1676 and 811 differentially expressed genes (DEGs) between the varieties E1 and C105 at 16 h and 64 h under drought stress, respectively. Six and nine KEGG pathways were significantly enriched at 16 h and 64 h under drought stress, which produced 40 and 184 nodes through protein-protein interaction (PPI) analysis, respectively. The DEGs of the PPI nodes were involved in the ABA (abscisic acid) and MAPK (mitogen-activated protein kinase) pathways, N-glycosylation, sulfur metabolism, and sugar metabolism. Furthermore, the ectopic overexpression of a key gene, AAT, encoding aspartate aminotransferase (AAT), in tobacco, enhanced drought tolerance. The activities of AAT and peroxidase (POD), the contents of cysteine and isoleucine, were increased, and the contents of malonaldehyde (MDA) and water loss decreased in the overexpressed plants. This study provides a novel insight into genetic response to drought stress and some candidate genes for drought tolerance genetic improvements in this plant.