Suppression of basal defenses in the syncytium of the cyst nematode Heterodera schachtii by Arabidopsis miR827
T. HEWEZI (1), S. Piya (2), M. Qi (3), B. Muthukumar (2), J. Rice (2) (1) University of Tennessee, U.S.A.; (2) University of Tennessee, U.S.A.; (3) Iowa State University, U.S.A.

Plant-parasitic cyst nematodes induce the formation of multinucleated feeding structures termed syncytia in the roots of host plants as the sole source for nematode nourishment. These sedentary endoparasites are involved in sophisticated biotrophic interactions for extended periods with host plants where suppression of basal defenses is critical for successful parasitism. However, the molecular mechanisms underlying suppression of immune responses in the syncytium remain largely unknown. In this study, we describe a new functional role of Arabidopsis miR827 and its NITROGEN LIMITATION ADAPTATION (NLA) target gene in suppressing plant immune response in the syncytium to facilitate plant susceptibility to the beet cyst nematode Heterodera schachtii. miR827 was activated in the initial feeding cells and this activation was sustained in the syncytium during all sedentary stages of nematode development. In the meantime, the NLA target gene was post-transcriptionally silenced in the syncytium, to permanently suppress its activity during all nematode parasitic stages. miR827 overexpression lines showed hyper-susceptibility phenotypes to H. schachtii with increases in susceptibility between 90 and 125% relative to the wild-type Col-0. Impeding NLA function resulted in significant increases in plant susceptibility, thereby phenocopying the miR827 overexpression lines. In contrast, suppression of miR827 activity through target mimicry or by overexpression a miR872-resistant cDNA of NLA produced the opposite phenotype of reduced plant susceptibility. Gene expression analysis of pathogenesis-related genes together with Agrobacterium–mediated transient expression in Nicotiana benthamiana provided strong evidence that NLA functions as a positive regulator of basal defense pathways. Thus, nematode–activated miR827 in the syncytium functions to suppress immune responses and facilitate infection.

Abstract Number: P9-259
Session Type: Poster