In the face of global climatic changes, exploring how plant adaptation and responses to drought vary among different regions is crucial to understand and predict its geographic distribution. In this study, to explore the drought adaptation and responses of the dominant species in the semi-arid Eurasian Steppes and their differences among the species distribution regions in terms of growth, physiology and RNA-seq transcriptome, Stipa krylovii was chosen as the study object and a seed source (3 regions: eastern, middle and western regions) × soil moisture treatment (3 treatments: control, light drought and heavy drought) two-factor experiment was conducted. (1) Four growth traits for individuals from the western region were significantly lower than those from the other two regions. By Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analysis on gene expressions of individuals from each treatment, unique enriched pathways were found mainly under heavy drought. (2) The decrease in the number of tillers with the increasing drought was much lower for individuals from the western region than those from the other two regions. By KEGG functional enrichment analysis on differentially expressed genes (DEGs) between heavy drought treatment vs control, enrichment pathways of individuals from the eastern and middle regions mainly regulated energy metabolism and metabolism of other amino acids; and those from the western region regulated biosynthesis of other secondary metabolites and carbohydrate metabolism. (3) Clustering analysis based on gene expressions separated the western region from the other two regions under the same soil moisture treatment. This study indicates that drought adaptation and response mechanisms of S. krylovii vary among different regions, especially between individuals from the western region and the other two regions. These findings are essential for us to understand the adaptive evolution of population and germplasm resource protection for this important species in semi-arid grasslands.

Epichloë endophytes can improve the resistance of host grasses to pathogenic fungi in grasslands. However, little is known about the mechanisms involved. We investigated the mechanisms underlying the effect of Epichloë sibirica on the resistance of Achnatherum sibiricum to Curvularia lunata by metabolomics approaches. The results demonstrated that before and after pathogen inoculation, 58 and 157 differential metabolites (DMs) were respectively induced by endophytes. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of DMs showed that amino acids and phenols were mostly accumulated by endophytic infection. Integrated transcriptome and metabolomics KEGG analysis revealed that plant hormone signal transduction was significantly enriched. After measurement, we found that endophytic infection increased jasmonic acid (JA) concentration before pathogen inoculation and increased ethylene (ET) and pipecolic acid concentration after pathogen inoculation. Exogenous phytohormones treatment verified that endophytes improved the disease resistance of A. sibiricum by promoting JA and ET accumulation. In phenylpropanoid synthetic pathway, the endophytes promoted the accumulation of ferulic acid, p-coumaroylagmatine, and feruloylputrescine which was related to resistance against plant disease. Overall, our research suggests that Epichloë endophytes presumably trigger induced systemic resistance of the hosts to pathogenic fungi via activating JA/ET signaling pathways and promoted antimicrobial phenol accumulation in hosts.

Epichloë endophytes can improve the resistance of host grasses to pathogenic fungi. However, little is known about the mechanisms involved. We studied the effect of Epichloë sibirica on the resistance of Achnatherum sibiricum to Curvularia lunata. Then, the global gene expression between endophyte-infected and endophyte-free leaves was compared. Finally, exogenous hormones were applied to verify the action mechanism of the endophyte. The endophyte improved pathogen resistance of host. Before pathogen inoculation, the endophyte had activated the host’s immunity by increasing jasmonic acid (JA) accumulation, and upregulating the expression of genes encoding pathogenesis-related proteins and EIN3/ERF1 transcription factors. After pathogen inoculation, the endophyte increased the accumulation of both JA and ethylene (ET), and amplified the gene response in the EIN3/ERF1 transduction pathway. Moreover, the endophyte altered the expression of genes encoding putative WRKY transcription factors and glutathione-S-transferase, which are related to disease resistance. Overall, this work first revealed that E. sibirica enhanced the resistance of A. sibiricum to C. lunata by inducing the response of EIN3/ERF1 transduction pathway regulated jointly by JA/ET. Before pathogen inoculation, the endophyte induced JA accumulation to improve constitutive resistance in the host. After pathogen inoculation, the endophyte enhanced the induced systemic resistance by promoting ET synthesis.