NH4+ Suppresses NO3–-Dependent Lateral Root Growth and Alters Gene Expression and Gravity Response in OsAMT1 RNAi Mutants of Rice (Oryza sativa)

Abstract

TheAMT1family comprises major ammonium transporters in rice roots. In this study, we utilizedAMT1RNAi mutants (amt1) to explore howAMT1affects NH4+- and NO3--mediated morphological development and NH4+-responsive gene expression in roots. In the presence of NH4+,amt1showed inhibition of NO3-- dependent lateral root development. The inhibitory action of NH(4)(+)on lateral root growth was independent of the NO(3)(-)concentrations supplied toamt1roots. The results of split root assays indicated that NH(4)(+)exerts systemic action in inhibiting NO3--dependent lateral root development inamt1. Further study with NAA and NOA, a potent auxin flux inhibitor, suggested that perturbation of membrane dynamics might not be the primary cause of the inhibitory action of NH(4)(+)on NO3--mediated lateral root growth inamt1mutants. RNA-seq analysis of NH4+-responsive genes showed that approximately half of DEGs observed in wild-type roots were not detected in the DEGs ofamt1roots. Gene ontology enrichment analysis suggested that the expression of specific functional gene groups were affected byamt1during the early response to NH4+. Auxin-responsive gene expression and root gravity responses were altered inamt1. This study demonstrated thatAMT1affects the interactions not only between ammonium and nitrate in lateral root growth but also between auxin and NH(4)(+)in rice roots.