Integrated transcriptomic and proteomic analyses reveal the impact of drought and heat stress combination on Morus alba

The mulberry (Morus alba L.) tree is an economically and ecologically important perennial woody plant. With climate change, heat, and drought stresses have become more frequent and intense in mulberry growing areas with a strong influence on phenology. However, how mulberry performs in terms of physiological responses under combined drought and heat stress is unknown. Here, we firstly studied the characteristics of three forage mulberry varieties (Guisangyou 62, Guisangyou 12, Yuesang 51) response to combined drought and heat stress (WD+HS) via integrated physiological, transcriptome and proteome profiles. Weighted gene co-expression network analysis (WGCNA) was conducted and we detected four important modules and 195 candidate genes between three cultivars related to WD+HS. 1795 differentially-expressed proteins (DEPs) and 329 proteins abundance changed significantly between three cultivars were identified by tandem mass tag (TMT) quantitative proteomic analysis. Finally, six genes including M.alba_G0006903 (HSP21), M.alba_G0008420 (HSP70T-2), M.alba_G0017894 (PPH), M.alba_G0019599 (BAG6), M.alba_G0007122 (MybSt1) and M.alba_G0012112 (GT2) in three cultivars were identified as candidate hub genes both in co-expression network and PPI network. These results lay a foundation for elucidating the molecular mechanism of the mulberry response to combined drought and heat stress.