Transcriptional repressor IAA17 is involved in nitrogen use by modulating cytosolic glutamine synthetase GLN1;2 in Arabidopsis roots

Nitrogen is an essential element for plant growth. Development of the root system architecture is highly correlated with nitrogen availability from the environment. Recent studies show that auxin response modules are involved in nitrate-dependent lateral root growth. However, the role of auxin in nitrogen metabolism remains to be elucidated. Few researchers have addressed the effect of auxin signaling modules on the use of ammonium for nutrition. The purpose of this study was to describe and examine the relation between auxin signaling modules and ammonium for nutrition. The growth of T-DNA insertion lines for auxin signaling modules was compared with that of a wild type under different nitrogen regimes. Nitrogen use efficiency consists of two components: metabolism and uptake. The nitrogen usage index was calculated following elemental analysis to evaluate nitrogen metabolism. Isotope-labeled ammonium uptake was measured under nitrogen-deficient and -sufficient conditions. Transcriptional levels and accumulation of enzymes necessary for primary ammonium assimilation, glutamine synthetase and glutamate synthase were evaluated. One of the T-DNA insertion lines for the auxin signaling module, IAA17, showed severe growth reduction in hydroponic solution containing ammonium as a major nitrogen source. The accumulation of cytosolic glutamine synthetase was reduced in the roots of iaa17. The expression of cytosolic glutamine synthetase 1;2 in iaa17 did not respond to ammonium supply. Here we show that the auxin signaling module has an effect on ammonium use by regulating the transcriptional level of cytosolic glutamine synthetase 1;2 in the root, the gene essential for ammonium assimilation.