The AAP gene family for amino acid permeases contributes to development of the cyst nematode Heterodera schachtii in roots of Arabidopsis

Abstract

The beet cyst nematode Heterodera schachtii is able to infect Arabidopsis plants and induce feeding sites in the root. These syncytia are the only source of nutrients for the nematodes throughout their life and are a nutrient sink for the host plant. We have studied here the role of amino acid transporters for nematode development. Arabidopsis contains a large number of different amino acid transporters in several gene families but those of the AAP family were found to be especially expressed in syncytia. Arabidopsis contains 8 AAP genes and they were all strongly expressed in syncytia with the exception of AAP5 and AAP7, which were slightly downregulated. We used promoter::GUS lines and in situ RT-PCR to confirm the expression of several AAP genes and LHT1, a lysine- and histidine-specific amino acid transporter, in syncytia. The strong expression of AAP genes in syncytia indicated that these transporters are important for the transport of amino acids into syncytia and we used T-DNA mutants for several AAP genes to test for their influence on nematode development. We found that mutants of AAP1, AAP2, and AAP8 significantly reduced the number of female nematodes developing on these plants. Our study showed that amino acid transport into syncytia is important for the development of the nematodes.

Keywords: Amino acid transporter; Arabidopsis; Heterodera schachtii; Roots; Syncytium.

Fig. 1

GUS analysis of infected and uninfected Arabidopsis roots of pAAP::GUS fusion lines. Uninfected roots and syncytia were stained for GUS activity at 5 and 15 dpi, respectively. The nematodes at 5 dpi were stained with acid fuchsin to ease observation and juveniles are marked with arrows.

Fig. 2

In situ RT-PCR for AAP genes. (+) = 15 dpi syncytia, (−) = negative control of 15 dpi syncytia, and uninfected = uninfected roots. The gene name on the left of each row shows the targeted gene (scale bar = 50 μm).

Fig. 3

Nematode infection assay for aap and lht1 mutants. Average numbers of females and males per cm root are shown with the standard error bar. The data are the average of all three independent repetitions. (a) Shows the results of the mutants with a Col genetic background and (b) shows the mutants with Ws genetic background. (*) marks the values with statistically significant difference to the wild type according to the LSD test at confidence level 90.0%.