OsAMT1;1 and OsAMT1;2 Coordinate Root Morphological and Physiological Responses to Ammonium for Efficient Nitrogen Foraging in Rice

Abstract

Optimal plant growth and development rely on morphological and physiological adaptions of root system to forage heterogeneously distributed nitrogen (N) in soils. Rice grows mainly in the paddy soil where ammonium (NH4+) is present as the major N source. Although root NH4+ foraging behaviors are expected to be agronomically relevant, the underlying mechanism remains largely unknown. Here, we showed that NH4+ supply transiently enhanced the high-affinity NH4+ uptake and stimulated lateral root (LR) branching and elongation. These synergistic physiological and morphological responses were closely related to NH4+-induced expression of ammonium transporters OsAMT1;1 and OsAMT1;2 in roots. The two independent double mutants (dko) defective in OsAMT1;1 and OsAMT1;2 failed to induce NH4+ uptake and stimulate LR formation, suggesting that OsAMT1s conferred the substrate-dependent root NH4+ foraging. In dko plants, NH4+ was unable to activate expression of OsPIN2, and OsPIN2 mutant (lra1) exhibited strong reduction in NH4+-triggered LR branching, suggesting that auxin pathway was likely involved in OsAMT1s-dependent LR branching. Importantly, OsAMT1s-dependent root NH4+ foraging behaviors facilitated rice growth and N acquisition under fluctuating NH4+ supply. These results revealed an essential role of OsAMT1s in synergizing root morphological and physiological processes, allowing for efficient root NH4+ foraging to optimize N capture under fluctuating N availabilities.

Root phenotypes for improved nitrogen capture

“…Increased root hair length and density is an important phenotype to investigate interactions of root anatomy with nitrification inhibitors, although rooting depth would also be logical to investigate given the gradient in concentrations of nitrogen compounds by soil depth. Further, plant responses to the increased ammonium resulting from the nitrification inhibition such as the proliferation of lateral roots (Wu et al 2022) would be interesting to assess in the cereals producing these compounds. This is a whole field of research open to be explored, with implications for targeting adaptive phenotypes in crop breeding that will reduce nitrogen losses in agricultural fields.…”