Auxin induction is a trigger for root gall formation caused by root-knot nematodes in white clover and is associated with the activation of the flavonoid pathway

Abstract

We studied the expression of the auxin responsive promoter (GH3) fused to the gusA reporter gene in white clover (Trifolium repens cv. Haifa) during the initiation of root galls by root-knot nematodes (Meloidogyne javanica) to investigate whether nematode infection affects auxin distribution in developing galls. In search for a plant signal that would mediate changes in auxin location we studied the induction of the flavonoid pathway because flavonoids can act as auxin transport regulators. Three chalcone synthase (CHS1, CHS2 and CHS3) promoter:gusA fusions were examined in transgenic plants and flavonoids were detected using fluorescence microscopy. Within 24 h post inoculation CHS:gusA expression occurred around the invading nematode. At 48 h post inoculation CHS:gusA expression and flavonoids were detected throughout the infection site, followed by high GH3:gusA expression in the gall 48–72 h post inoculation. Initially (48–72 h post inoculation) high GH3:gusA expression in giant cell precursors was followed by low expression in the enlarging giant cells (96–120 h post inoculation), suggesting that auxin is needed as a trigger for giant cell initiation but not for later enlargement. We suggest that nematodes control auxin distribution in the root and that flavonoids could be responsible for controlling auxin accumulation.

Comprehensive Transcriptome Profiling in Tomato Reveals a Role for Glycosyltransferase in Mi-Mediated Nematode Resistance

“…We did, however, observe significant differential regulation of shikimate pathway genes later in the infection cycle (i.e. in roots with established feeding sites), consistent with the notion that global alterations of auxin balance accompany RKN infection in general (Hutangura et al, 1999). Table III.…”

“…Because Mi-mediated resistance is effected within a narrow time window after RKN invasion (Dropkin, 1969), this result was not surprising. We also found no differences in gene expression (Hutangura et al, 1999;Bird and Koltai, 2000); 3, pathogenesis-related genes (Bowles, 1990); 4, transport (Hammes et al, 2005); 5, nucleic acid binding; 6, (I) shikimate (Doyle and Lambert, 2002); 7, (Y) cell cycle (Niebel et al, 1996;de Almeida Engler et al, 1999); 8, aquaporin, water channel-related genes (Opperman et al, 1994); 9, (X) peroxidase; 10, cell wall (Bird,1974); 11, GC genes ; 12, (S) ribosome-related genes; and 13, genes with unknown function. Annotations were searched with keywords (Supplemental Table S2) to identify genes to categorize.…”

“…Various lines of evidence also have implicated auxin and cytokinin flux in the RKN-host interaction (Mathesius et al, 1998;Hutangura et al, 1999;Karczmarek et al, 2004;Lohar et al, 2004) as part of the regulation of root architecture. Thus, rather than focus on gene expression in GCs per se, we designed experiments to interrogate genes representative of the broader tomato root transcriptome during compatible and incompatible interactions with RKN.…”

Uptake and translocation of nitrogen, phosphorus and calcium in soybean infected with Meloidogyne incognita and M. javanica

“…The decrease in the shoot mass seems to be very closely related to the root growth, and might be a consequence of the strong carbon sink represented by gall formation and the emission of new secondary roots (Oteifa & Elgindi, 1962;Wallace, 1971;Hutangura et al, 1999). Decrease of photosynthesis in plants infected by nematodes has been observed by several authors (Hussey, 1985;Melakeberhan et al;1985).…”

“…Although increase of the mass of root systems infected by root-knot nematodes has been reported (Wallace, 1971;Carneiro et al, 1999), there is no information available concerning the relative contribution of secondary roots and galls. Formation of new secondary roots subsequent to the presence of nematodes was studied by Hutangura et al (1999), suggesting the participation of increased levels of plant hormones.…”