Epichloë gansuensis Increases the Tolerance of Achnatherum inebrians to Low-P Stress by Modulating Amino Acids Metabolism and Phosphorus Utilization Efficiency

Abstract

In the long-term evolutionary process, <i>Achnatherum inebrians</i> and seed-borne endophytic fungi, <i>Epichloë gansuensis</i>, formed a mutually beneficial symbiosis relationship, and <i>Epichloë gansuensis</i> has an important biological role in improving the tolerance of host grasses to abiotic stress. In this work, we first assessed the effects of <i>Epichloë gansuensis</i> on dry weight, the content of C, N, P and metal ions, and metabolic pathway of amino acids, and phosphorus utilization efficiency (PUE) of <i>Achnatherum inebrians</i> at low P stress. Our results showed that the dry weights, the content of alanine, arginine, aspartic acid, glycine, glutamine, glutamic acid, L-asparagine, lysine, phenylalanine, proline, serine, threonine, and tryptophan were higher in leaves of <i>Epichloë gansuensis</i>-infected (E+) <i>Achnatherum inebrians</i> than <i>Epichloë gansuensis</i>-uninfected (E-) <i>Achnatherum inebrians</i> at low P stress. Further, <i>Epichloë gansuensis</i> increased C content of roots compared to the root of E- plant at 0.01 mM P and 0.5 mM P; <i>Epichloë</i><i>gansuensis</i> increased K content of leaves compared to the leaf of E- plant at 0.01 mM P and 0.5 mM P. <i>Epichloë</i><i>gansuensis</i> reduced Ca content of roots compared to the root of E- plant at 0.01 mM P and 0.5 mM P; <i>Epichloë gansuensis</i> reduced the content of Mg and Fe in leaves compared to the leaf of E- plant at 0.01 mM P and 0.5 mM P. In addition, at low P stress, <i>Epichloë gansuensis</i> most probably influenced aspartate and glutamate metabolism; valine, leucine, and isoleucine biosynthesis in leaves; and arginine and proline metabolism; alanine, aspartate, and glutamate metabolism in roots. <i>Epichloë gansuensis</i> also affected the content of organic acid and stress-related metabolites at low P stress. In conclusion, <i>Epichloë gansuensis</i> improves <i>Achnatherum inebrians</i> growth at low P stress by regulating the metabolic pathway of amino acids, amino acids content, organic acid content, and increasing PUE.