Coherent regulation of miR167a biogenesis and expression of auxin signaling pathway genes during bacterial stress in tomato

Several miRNAs have been implicated in plant stress response. However, the specific role and physiological effect caused by most of these miRNAs during biotic stress remains elusive. Particularly, the significance of differential regulation of a development-related miRNA under stress in mature leaves has not been studied. We have explored the regulation of miR167a, its targets ARF6/8 and related auxin signaling pathway during biotrophic Xanthomonas campestris, pv. vesicatoria and hemi-biotrophic Pseudomonas syringae pv. DC3000 pathogen infections in tomato plant. miR167a was upregulated during both the infections at varied extent, and the expression of its targets ARF6 and 8 were inversely correlated in infected leaves. Flg22 treatment also yielded similar upregulation. Further analysis of expression level of primary transcripts of MIR167a indicated both transcriptional and processing regulations were important in maintaining the mature miR167a level in infected tissues. Although bacterial PAMP was sufficient in inducing miR167a upregulation, the extent of regulation was determined by active infection. Alteration of expression of genes of host auxin signaling pathway and which are likely regulated by ARF6/8, were also associated with the stress response. This study underscores the importance of miR167a mediated regulation of auxin signaling genes during biotic stresses in tomato.