Professor National Taiwan University Taipei, Taipei, Taiwan (Republic of China)
Body of Abstract: Beneficial endophytic fungi colonized with plants would promote host growth and production. It has also been found that some endosymbiotic microorganisms are helpful in enhancing hosts’ abiotic and biotic stress tolerance. However, the interactions between endophytes, plants and environmental factors remain unclear. Pirifomospora indica (P. indica) is a root endophytic fungi with a broad host spectrum. Our study found that P. indica colonization would recover the changes in rice seminal root growth conducted by nitrogen deficiency treatments. The seminal root length of rice seedlings cultured in a nutrient solution without nitrogen sources was significantly longer than in the control condition. However, the nitrogen-deficiency stimulated elongation phenomenon was not presented in P. indica-inoculated seedling roots. To reveal the mechanisms of P. indica-repressed nitrogen deficiency-induced root growth, the transcriptome of root samples collected from seedlings treated with nitrogen deficiency, P. indica inoculation, and co-treatment were analyzed. The number of up-regulated auxin-related genes was significantly higher than that of down-regulated genes in plants grown under nitrogen deficiency conditions. On the other hand, the down-regulated ethylene-related genes were more than the up-regulated genes. Most of these hormone-related genes whose responses to nitrogen deficiency would be attenuated in P. indica-colonized roots, such as auxin-responsive genes OsSAUR27 and OsSAUR28, ethylene-responsive genes OsACO5. It was suggested that P. indica modulated the nitrogen deficiency-induced root growth were mediated the regulation of hormone signaling.