Abstract
Although it is well established that flavonoid synthesis is induced in diverse plant species during nematode parasitism, little is known about the regulation of genes controlling flavonol biosynthesis during the plant–nematode interaction. In this study, expression of the Arabidopsis thaliana flavonol-specific transcription factor, AtMYB12, the flavonol synthase genes, AtFLS1, 2, 3, 4, and 5, and the gene encoding the central flavonoid enzyme, chalcone synthase (AtCHS), were examined in plant roots during infection by Heterodera schachtii (sugar beet cyst) and Meloidogyne incognita (root-knot) nematodes. These experiments showed that AtMYB12 was transiently upregulated at 9 dpi in syncytia associated with sugar beet cyst nematode infection and that an Atmyb12-deficient line was less susceptible to the parasite. This suggests that, rather than contributing to plant defense, this gene is essential for productive infection. However, the AtCHS and AtFLS1 genes, which are controlled by AtMYB12, did not exhibit a similar transient increase, but rather were expressly downregulated in syncytia relative to adjacent uninfected root tissue. Genetic analyses further indicated that AtFLS1 contributes to plant defense against Cyst nematode infection, while other AtFLS gene family members do not, consistent with prior reports that these other genes encode little or no enzyme activity. Together, these findings indicate a role of AtMyb12 in promoting the early stages of Cyst nematode infection, while flavonols produced through the action of AtFLS1 are essential for plant defense. On the other hand, a transient induction of AtMYB12 was not observed in galls produced during root-knot nematode infection, but this gene was instead substantially downregulated, starting at the 9 dpi sampling point, as were AtCHS and AtFLS1. In addition, both the AtMYB12- and AtFLS1-deficient lines were more susceptible to infection by this parasite. There was again little evidence for contributions from the other AtFLS gene family members, although an AtFLS5-deficient line appeared to be somewhat more susceptible to infection. Taken together, this study shows that sugar-beet cyst and root-knot nematodes modulate differently the genes involved in flavonol biosynthesis in order to successfully infect host roots and that AtFLS1 may be involved in the plant basal defense response against nematode infection.
Highlights
Plant parasitic nematodes are the causal agents of an estimated USD 100 billion in crop losses to the world-wide agro-economy annually, with Cyst (Heterodera and Globodera spp.) and root-knot (Meloidogyne spp.) nematodes causing the most extensive damage [1]
M. incognita expression examined by histochemical staining histochemical staining at 9experiment dpi. The results of this thatisexpression at 9 dpi. The results of this indicate that experiment expression ofindicate upregulatedofinAtMYB12 syncytia is upregulated in syncytia formed schachtiidownregulated (Figure 1C) butinstrongly downregulated in galls formed by H. schachtii
Our results showed that expression of AtFLS2, AtFLS3, and AtFLS4 increased during H. schachtii infection, while expression of AtFLS5 did not change (Figure 4A)
Summary
Plant parasitic nematodes are the causal agents of an estimated USD 100 billion in crop losses to the world-wide agro-economy annually, with Cyst (Heterodera and Globodera spp.) and root-knot (Meloidogyne spp.) nematodes causing the most extensive damage [1]. Cyst and root knot nematodes induce the expression of different genes in Arabidopsis thaliana roots [7,12]. This is likely to be a reflection of the different modes of parasitism between cyst and root-knot nematodes as reflected in feeding cell ontogeny. In the study presented here, quantitative real-time PCR was used to analyze the expression patterns of AtMYB12 and the flavonoid biosynthetic genes, AtCHS and AtFLS1-5 during Arabidopsis parasitism by the beet cyst nematode, Heterodera schachtii and the southern root-knot nematode, Meloidogyne incognita. Hypothesis hypothesis is that sugar beet cyst and root knot nematodes modulate the expression of genes is that sugar beet cyst and root knot nematodes modulate the expression of genes involved in the involved in the biosynthesis of flavonols in orderinfect to successfully biosynthesis of flavonols in order to successfully host roots.infect host roots
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