sp. IRBG74 Alters Root Development by Affecting Auxin Signaling.

sp. IRBG74 not only nodulates but also can enhance rice growth; however, the underlying molecular mechanisms are not clear. Here, we show that sp. IRBG74 colonizes the roots of , which leads to inhibition in the growth of main root but enhancement in the formation of lateral roots. The promotion of lateral root formation by sp. IRBG74 in the mutant, which is insensitive to flagellin, is similar to the wild-type plant, while the auxin response deficient mutant is significantly less sensitive to sp. IRBG74 than the wild type in terms of the inhibition of main root elongation and the promotion of lateral root formation. Further transcriptome analysis of roots inoculated with sp. IRBG74 revealed differential expression of 50 and 211 genes at 24 and 48 h, respectively, and a majority of these genes are involved in auxin signaling. Consistent with the transcriptome analysis results, sp. IRBG74 treatment induces expression of the auxin responsive reporter in roots. Our results suggest that in sp. IRBG74 colonizes roots and promotes the lateral root formation likely through modulating auxin signaling. Our work provides insight into the molecular mechanisms of interactions between legume-nodulating rhizobia and non-legume plants.