Physiological and transcriptome analysis reveals key genes and molecular basis into heterosis of kenaf (Hibiscus cannabinus L.) under drought stress

Kenaf exhibits strong heterosis with abiotic stress tolerance. To understand the performance of kenaf heterosis under drought stress, transcriptome profiling was performed by RNA sequencing of kenaf hybrid F1 and its parents (CP079 and CP071). Under drought stress, SPAD values, soluble sugar, and proline accumulation were significantly higher, while malonaldehyde (MDA) content were lower in the F1 hybrid compared with its parents. In addition, F1 exhibited higher activity of antioxidant enzymes. Overall, 616 common differentially expressed genes (DEGs) closely related to drought tolerance and 792 specific genes related to drought heterosis were identified between the F1 hybrid and its parents. The expression patterns of 524 and 523 DEGs were closer to maternal and paternal genes, respectively. Some critical drought-induced transcription factors (TFs) of specific drought-associated genes such as MYB, bHLH, NAC, bZIP, and HSP families played key roles in drought stress tolerance heterosis. According to KEGG pathway analysis, DEGs are primarily involved in the metabolism of galactose, starch and sucrose, glycerolipids, taurine, and hypotaurine, plant MAPK signaling pathway and the transduction of plant hormones. Moreover, several hormone transduction genes among the drought stress heterosis genes were found, including HcGH3, HcEXPB4, HcVAP, HcCKX1, HcDnaJ, and HcMSR2. Furthermore, overexpression HcERF2 suggested it positively regulates the drought tolerance by increasing antioxidant enzyme activity. These findings provide a solid foundation for understanding the essential genes functions and pathways involved in kenaf heterosis during drought stress.