A role for the gene regulatory module miRNA172/TOE1/FT in the feeding sites induced by Meloidogyne javanica in Arabidopsis

Root knot nematodes (RKNs) penetrate into the root vascular cylinder triggering morphogenetic changes to induce galls, de novo formed ‘pseudo-organs’ containing several giant cells (GCs). Distinctive gene repression events observed in early gall/GCs development is thought to be mediated by post-transcriptional silencing via -miRNAs, a process far from being fully characterized. Arabidopsis backgrounds with altered activities based on target MIMICRY ( 35S::MIM172 ), 35S::TOE1-miR172-resistant ( 35S::TOE1 R ) and mutant ( ft-10 ) lines, were used for functional analysis of nematode infective and reproductive parameters. GUS-reporter lines, MIR172A-E::GUS , auxin (IAA) and auxin-inhibitor (PEO-IAA) treatments, as well as a MIR172C AuxRE− ::GUS line with two mutated auxin responsive elements ( AuxREs ) were assayed for nematode-dependent gene expression. Arabidopsis backgrounds with altered expression of either MIRNA172, TARGET OF EAT1 ( TOE1 ), and FLOWERING LOCUS T ( FT ), showed lower susceptibility to the RKNs and smaller feeding sites, galls/GCs. MIR172C-D::GUS showed restricted activity in galls/GCs that is regulated by auxins through auxin responsive factors. IAA induced their activity in galls while PEO-IAA treatment and mutations in AuxRe motifs abolished it. The results show that the activity of the regulatory module miRNA172/TOE1/FT plays an important role in correct GCs and gall development where miRNA172 is modulated by auxins.