microRNA Expression Analysis in Wheat (Triticum aestivum) Seedling Inoculated with Endophytic Rhizobia Azorhizobium caulinodans ORS571

Azorhizobium caulinodans ORS571, a novel rhizobia, can form endosymbionts with its nature host Sesbania rostrata roots and stems. Recent studies show that A. caulinodans ORS571, as endophytic rhizobia, also can disseminate and colonize inside of cereal plants. However, the regulatory mechanism is unknown. MicroRNAs (miRNAs) are small, endogenous RNAs that regulate gene expression at the post-transcriptional levels. In this study, wheat cv. Xiaoyan22 seedlings were inoculated with gfp labeled A. caulinodans ORS 571. Confocal microscopy images showed that labeled A.caulinodans ORS 571 could colonize in roots and leaves of wheat seedling. The expression pattern of 15 conserved miRNAs in both roots and shoots was determined at 6 different time stages post inoculation. Our results show that endophytic rhizobia induced miRNA expression progressively with a peak at the 12-24 hours after treatment. miRNA expression was tissue-dependent. Some miRNAs, such as miR 156 and miR 160 responded more in roots than in leaves. In contrast, some miRNAs, such as miR 171 and miR 398 responded higher in leaves than that in roots. These miRNAs showed dynamic expression patterns and their expression level peaked at different time points. This results suggest that these miRNAs could be responsive to A. caulinodans infection and could involve in plant growth, nutrient metabolisms and plant-rhizobia interactions.