The study of the contribution of the plant defence hormones, salicylic acid (SA) and jasmonic acid (JA), in the resistance against pathogens of plants associated with Epichloë fungal endophytes has been scanty. We hypothesised that Epichloë spp., capable of inducing host plant SA-dependent defences, would increase the levels of plant resistance against biotrophic pathogens. Plants of Achnatherum inebrians, with and without the fungal endophyte Epichloë gansuensis, were inoculated with the biotrophic fungal pathogen Blumeria graminis. We measured the status of plant defences (associated with SA and JA signalling pathways) and the levels of resistance to the pathogen. Plants associated with the endophyte showed less disease symptoms caused by the biotrophic pathogen than plants without the endophyte. In agreement with our hypothesis, the Epichloë endophyte increased the plant production of SA and enhanced the expression levels of plant genes of synthesis and response to the SA hormone. The elevated expression of SA-related genes coding for putative plant enzymes with anti-fungal activities promoted by the endophyte may explain the enhanced resistance to the pathogen. The present study highlights that interaction between the plant immune system and Epichloë fungal endophytes can contribute significantly to the resistance of endophyte-symbiotic plants against pathogens.

The present study was designed to explore the effects of the endophyte Epichloë gansuensis on gene expression related to plant hormone biosynthesis and response pathways and the content of salicylic acid (SA) and jasmonic acid (JA) hormones of Achnatherum inebrians, under different moisture conditions. Through a pot experiment and transcriptome analysis, we found a total of 51 differentially expressed genes (DEGs) related to hormone biosynthesis and response pathways, including 12 auxin related genes, 8 cytokinin (CTK) related genes, 3 gibberellin (GA) related genes, 7 abscisic acid (ABA) related genes, 7 ethylene (ET) related genes, 12 JA related genes and 4 SA related genes. Furthermore, key genes of JA and SA biosynthesis and response pathways, such as LOX2S, AOS, OPR, ACX, JMT, JAZ, PAL, NPR1, TGA and PR-1, showed different degrees of upregulation or downregulation. Under 60% soil moisture content, the JA content of endophyte-free (EF) A. inebrians was significantly (p < 0.05) higher than that of endophyte-infected (EI) A. inebrians. Under 30% and 60% soil moisture content, the SA content of EF A. inebrians was significantly (p < 0.05) higher than that of EI A. inebrians. SA content of EI A. inebrians under 30% and 60% soil moisture content was significantly (p < 0.05) higher than that under 15% soil moisture content. With both EI and EF plants, the SA and JA levels, respectively, are very similar at 15% soil moisture content. This study has revealed that E. gansuensis differentially activated plant hormone synthesis and signal transduction pathways of A. inebrians plants under different soil moisture availability.

The cuticular wax serves as the outermost hydrophobic barrier of plants against nonstomatal water loss and various environmental stresses. An objective of this study was to investigate the contribution of the mutualistic fungal endophyte Epichloë gansuensis to leaf cuticular wax of Achnatherum inebrians under different soil moisture availability. Through a pot experiment and gas chromatography−mass spectrometry (GC−MS) analysis, our results indicated that the hydrocarbons were the dominant components of leaf cuticular wax, and the proportion of alcohols, aldehydes, amines, and ethers varied with the presence or absence of E. gansuensis and different soil moisture availability. Amines and ethers are unique in endophyte-free (EF) A. inebrians plants and endophyte-infected (EI) A. inebrians plants, respectively. By transcriptome analysis, we found a total of 13 differentially expressed genes (DEGs) related to cuticular biosynthesis, including FabG, desB, SSI2, fadD, BiP, KCS, KAR, FAR, and ABCB1. A model is proposed which provides insights for understanding cuticular wax biosynthesis in the association of A. inebrians plants with E. gansuensis. These results may help guide the functional analyses of candidate genes important for improving the protective layer of cuticular wax of endophyte-symbiotic plants.

Cuticular wax plays a critical role as a plant protectant against various environmental stresses. We predicted that the presence of the mutualistic fungal endophyte Epichloë gansuensis in Achnatherum inebrians would change both the composition of leaf cuticular wax as plants aged during the growing season and the gene expression levels associated with the wax biosynthesis pathway. Endophyte-infected (EI) and endophyte-free (EF) A. inebrians plants were established for a four-month pot experiment. In agreement with our prediction, the presence of E. gansuensis can change the composition of leaf cuticular wax at different growing periods, particularly the proportion of esters, fatty acids and hydrocarbons. The proportion of fatty acids in EI plants was lower than that in EF plants. The proportion of hydrocarbons increased and esters decreased as plants grew. Furthermore, we found 11 DEGs coding for proteins involved in cuticular wax biosynthesis, including FabF, FAB2, ECR, FAR, CER1, ABCB1 and SEC61A. The present study highlights the significant contribution of E. gansuensis to leaf cuticular wax composition and biosynthesis in A. inebrians plants.