Evaluation of Drought Tolerance and Trehalose Response in Auricularia heimuer

Auricularia heimuer is drought tolerant, but the mechanism underlying its physiological response to drought has not been systematically studied. We selected 13 strains of A. heimuer and simulated drought stress using a complete yeast medium (CYM) containing 20% polyethylene glycol (PEG), while the medium used for the control treatments did not contain PEG. Strains were cultured on a shaker incubator at 25 °C at 120 rpm for 15 days under dark conditions. The contents of soluble sugars (SS) and soluble proteins (SP), the activities of superoxide dismutase (SOD) and catalase (CAT), the content of malondialdehyde (MDA), and the biomass were measured. Between the 20% PEG treatment and the control, as well as among different strains, there were significant differences in all of the physiological indices. The tested strains were classified into the following four categories according to their membership function values: the first category consisted of the highly drought-tolerant strain A; the second consisted of the drought-tolerant strains A127 and C; the third consisted of the moderately drought-tolerant strains A124, A14, A386, A462, A184, A496, A125, and B; and the fourth consisted of the drought-sensitive strains A356 and A508. Transcriptome analysis was performed on C before and after drought stress treatment, and 1762 differentially expressed genes (DEGs) were obtained, including 798 up- and 964 down-regulated genes. Through KEGG enrichment analysis, it was found for the first time that the synthesis pathway for trehalose in A. heimuer is trehalose phosphate synthase–trehalose phosphate phosphatase (TPS-TPP), which is involved in the response of A. heimuer to drought stress. In addition, two key enzyme genes involved in trehalose synthesis, namely trehalose-6-phosphate synthase (AhTPS) and trehalose-6-phosphate phosphatase (AhTPP), were significantly up-regulated after drought stress. The trehalose content significantly increased in 11 strains after drought stress treatment. This study discovered, for the first time, that the synthesis pathway of trehalose is involved in the response of edible fungi to drought stress, thus providing a reference for the genetic improvement of A. heimuer and the selection of drought-tolerant strains, laying a theoretical foundation for the resistance breeding of other edible fungi.