Overexpression of the transcription factor RAP2.6 leads to enhanced callose deposition in syncytia and enhanced resistance against the beet cyst nematode Heterodera schachtiiin Arabidopsis roots

Abstract

BackgroundCyst nematodes invade the roots of their host plants as second stage juveniles and induce a syncytium which is their source of nutrients throughout their life. A transcriptome analysis of syncytia induced by the beet cyst nematode Heterodera schachtii in Arabidopsis roots has shown that gene expression in the syncytium is different from that of the root with thousands of genes upregulated or downregulated. Among the downregulated genes are many which code for defense-related proteins. One gene which is strongly downregulated codes for the ethylene response transcription factor RAP2.6. The genome of Arabidopsis contains 122 ERF transcription factor genes which are involved in a variety of developmental and stress responses.ResultsExpression of RAP2.6 was studied with RT-PCR and a promoter::GUS line. During normal growth conditions the gene was expressed especially in roots and stems. It was inducible by Pseudomonas syringae but downregulated in syncytia from a very early time point on. Overexpression of the gene enhanced the resistance against H. schachtii which was seen by a lower number of nematodes developing on these plants as well as smaller syncytia and smaller female nematodes. A T-DNA mutant had a reduced RAP2.6 transcript level but this did not further increase the susceptibility against H. schachtii. Neither overexpression lines nor mutants had an effect on P. syringae. Overexpression of RAP2.6 led to an elevated expression of JA-responsive genes during early time points after infection by H. schachtii. Syncytia developing on overexpression lines showed enhanced deposition of callose.ConclusionsOur results showed that H. schachtii infection is accompanied by a downregulation of RAP2.6. It seems likely that the nematodes use effectors to actively downregulate the expression of this and other defense-related genes to avoid resistance responses of the host plant. Enhanced resistance of RAP2.6 overexpression lines seemed to be due to enhanced callose deposition at syncytia which might interfere with nutrient import into syncytia.

Mechanisms underlying the enhanced biomass and abiotic stress tolerance phenotype of an Arabidopsis MIOX over‐expresser

“…Over‐expression of RAP2.6 resulted in increased resistance to nematode ( Heterodera schachttii ) in A . thaliana by enhanced callose deposition (Ali, Abbas, Kreil, & Bohlmann, ).…”

The Impact of Plant-Parasitic Nematodes on Agriculture and Methods of Control

“…Although the cuticle is generally believed to be devoid of chitin, it is possible that chitin derivatives or chitin previously deposited in the stylet are recognized by the host which activates callose deposition at the site of penetration. The overexpression of the ethylene response transcription factor RAP2.6 in Arabidopsis enhanced plant basal resistance to H. schachtii [112]. Increased expression of jasmonic acidrelated genes and callose deposition were observed at nematode infection sites.…”

Plant-nematode Interactions: From Genomics to Metabolomics

“…It resulted in enhanced nematode resistance in overexpression lines (Ali et al, 2013a). The resistance in AtRAP2.6 overexpression lines was mediated by enhanced callose deposition and increased expression of JA inducible genes.…”

“…During compatible plant-nematode interaction, nematodes are somehow able to suppress the defense related genes. The overexpression of these genes has led to enhanced nematode resistance (Ali, 2012;Ali et al, 2013a). It could be an interesting starting point for further studies to explicate how nematodes are able to suppress systemic plant defense mechanisms.…”