Early transcriptomic events in microdissected Arabidopsis nematode-induced giant cells

Abstract

Summary Root‐knot nematodes differentiate highly specialized feeding cells in roots (giant cells, GCs), through poorly characterized mechanisms that include extensive transcriptional changes. While global transcriptome analyses have used galls, which are complex root structures that include GCs and surrounding tissues, no global gene expression changes specific to GCs have been described. We report on the differential transcriptome of GCs versus root vascular cells, induced in Arabidopsis by Meloidogyne javanica at a very early stage of their development, 3 days after infection (d.p.i.). Laser microdissection was used to capture GCs and root vascular cells for microarray analysis, which was validated through qPCR and by a promoter‐GUS fusion study. Results show that by 3 d.p.i., GCs exhibit major gene repression. Although some genes showed similar regulation in both galls and GCs, the majority had different expression patterns, confirming the molecular distinctiveness of the GCs within the gall. Most of the differentially regulated genes in GCs have no previously assigned function. Comparisons with other transcriptome analyses revealed similarities between GCs and cell suspensions differentiating into xylem cells. This suggests a molecular link between GCs and developing vascular cells, which represent putative GC stem cells. Gene expression in GCs at 3 d.p.i. was also found to be similar to crown galls induced by Agrobacterium tumefaciens, a specialized root biotroph.

A survey of genes involved in Arachis stenosperma resistance to Meloidogyne arenaria race 1

“…However, throughout the assay, an increase in expression was observed, and 79% of the genes were upregulated at 9 DAI. These results agree with the expression profiles reported during root-knot nematode infection in Arachis (Guimarães et al 2010;Tirumalaraju et al 2011) and other plants, such as rice (Kyndt et al 2012), Arabidopsis (Jammes et al 2005;Barcala et al 2010), tomato (Portillo et al 2013) and cowpea (Das et al 2010). These studies reported gene repression or constant expression at early stages of nematode-plant interaction, followed by a trend towards an increasing number of upregulated genes in both compatible and incompatible interactions.…”

“…In parallel to auxins, cytokinins also have been shown to play an important role in root-knot nematode gall formation, with high levels of expression induced in the early stages of plantparasite interaction (Goverse et al 2000;Barcala et al 2010). Cytokinin dehydrogenase (CKX) expression is induced by cytokinins, representing a negative feedback system, in which the accumulation of cytokinin induces its own catabolism, controlling the levels of the hormone in the cell .…”

Not to be suppressed? Rethinking the host response at a root-parasite interface

“…However, genome-wide profiling studies of different plant hosts during this post-induction/early nutrient acquisition 8 stage of infestation appear to support the general consensus for a suppression or absence of host defense signaling in giant cells induced by root-knot nematodes. In a microarray analysis of giant cells isolated from Arabidopsis roots at 3 days, genes included within the biotic stress functional category were in a general trend toward reduced transcript accumulation when compared to vascular tissues of non-infested root sections [24]. Similar results were also observed in giant cells isolated from infected tomato roots at 3 days and compared to vascular cells from non-infested roots [21].…”

“…Due to the fact that infestation sites are generally already well developed by 7 days, it is difficult to distinguish whether changes at these stages are a local response to pathogen invasion, a systemic response to the infestation itself or an endogenous response to altered plant metabolism. Within the giant cells themselves, the general trend is clearer than that for surrounding tissues and the majority of differentially expressed defense-related genes were found to be down-regulated throughout the nutrient acquisition stage [21,24].…”

“…These observed trends for defense-related genes do become inconsistent however when the analyses include the root tissue surrounding the giant cells. Several pathogenesis-related and wound-related genes that were repressed in giant cells were not differentially expressed in surrounding cells, whereas other stress-related genes that did not change in giant cells were either repressed or induced in the surrounding cells as determined by comparing whole galls to non-infested root fragments [21,24]. Biotic stress-related genes were not differentially expressed or had reduced transcript accumulation in infested rice roots compared to non-infested root tips at similar early time points, although conflicting responses of both induction and repression were observed within the jasmonate pathway [25,26].…”