AATRhg1 is a tonoplast protein that alters amino acid, metabolic, and defense responses and nematode resistance.

Abstract

Soybean cyst nematode (SCN, Heterodera glycines [HG]) causes significant soybean yield losses. The Rhg1 locus is a major contributor to SCN resistance and contains 3 genes that mediate this trait, including Rhg1-GmAAT (Glyma.18G022400), which encodes the putative amino acid transporter AATRhg1. The molecular function of AATRhg1 in SCN resistance is not understood. In this study, rhg1-b soybean lines with Rhg1-GmAAT silencing demonstrated that Rhg1-GmAAT can contribute to resistance against HG 0 SCN and also against problematic HG 2.5.7 populations that partially overcome rhg1-b-mediated resistance. When 2 previously characterized AATRhg1 mutants with contrasting effects on amino acid and betalain accumulation were tested for SCN resistance, the AATRhg1 Y268L mutant complemented SCN resistance in Rhg1-GmAAT-silenced plants, while the D122A mutant did not. Overexpression of Rhg1-GmAAT was not sufficient to enhance SCN resistance, suggesting that AATRhg1 requires coordinated activity with other proteins or pathways. Confocal microscopy demonstrated that AATRhg1 localizes to the tonoplast in soybean root cells. Amino acid, transcriptomic, and metabolomic profiles were determined for root segments collected 3 d after mock or SCN inoculation. In Rhg1-GmAAT-silenced rhg1-b plants relative to fully resistant (non-silenced) rhg1-b plants, levels of leucine, isoleucine, and tyrosine were significantly elevated. Rhg1-GmAAT silencing reduced SCN-responsive transcript abundances for multiple processes, significantly including genes for mitogen-activated protein kinase (MAPK) signaling, ethylene-associated responses, and starch and sucrose metabolism. The most common identified metabolomic changes were in amino acid derivatives, shikimate/phenylpropanoid/isoflavonoid compounds, terpenoids, and especially fatty acids. These findings can guide further investigation into the mechanisms by which AATRhg1 contributes to SCN resistance.