Integrated Physiological and Transcriptome Analyses of Wild Jujube (Ziziphus jujuba var. spinosa) Under Drought Stress

Drought stress is a significant environmental factor affecting plant growth, fruit quality and distribution. Wild jujube is an important species of eco-economic forest tree. In this study, two wild jujube families, 'NO. 1' (tolerant) and 'NO. 5' (sensitive), which show significant differences in morphological and physiological indicators in drought treatment, are considered. Compared with the 'NO. 5', the 'NO. 1' exhibited lower water loss, leaf yellowing and abscission rates, as well as reduced malondialdehyde (MDA) content, while showing higher superoxide dismutase (SOD) activity and elevated levels of soluble sugars (SS), soluble proteins (SP), and proline (Pro). In contrast, the 'NO. 5' suffered more severe damage to leaf epidermal cells compared with the 'NO. 1', accompanied by a significant decline in net photosynthetic rate (A) and instantaneous water use efficiency (WUEi). Transcriptomic profiles between two wild jujube families with markedly different drought responses (withholding water for 15 days) are shown. The two wild jujube families included 3238 up-regulated and 2675 down-regulated differentially expressed genes (DEGs). Many DEGs enriched in the GO and KEGG pathways are related to antioxidant activity, transmembrane transport, carbohydrate biosynthesis and metabolism, plant hormones, and photosynthesis. The biosynthesis of amino acids, the MAPK signaling pathway, plant hormone signal transduction, and flavonoid and alkaloid biosynthesis were the transcriptome modifications most significantly altered by drought stress. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to verify the precision of the RNA-seq data. ZjJIP23-1, ZjbZIP53, ZjSPS8, ZjCAO, ZjADH1 and ZjERF39 may play important roles in the drought tolerance of the wild jujube. This study provides a solid foundation for further studies on the complex mechanisms and breeding of drought-resistant plants in wild jujube.