ABA plays a central role in mediating the regulatory effects of nitrate on root branching in Arabidopsis

Abstract

SummaryThe formation of lateral roots (LR) is a major post-embryonic developmental event in plants. In Arabidopsis thaliana, LR development is inhibited by high concentrations of NO 3 ± . Here we present strong evidence that ABA plays an important role in mediating the effects of NO 3 ± on LR formation. Firstly, the inhibitory effect of NO 3 ± is signi®cantly reduced in three ABA insensitive mutants, abi4-1, abi4-2 and abi5-1, but not in abi1-1, abi2-1 and abi3-1. Secondly, inhibition by NO 3 ± is signi®cantly reduced, but not completely abolished, in four ABA synthesis mutants, aba1-1, aba2-3, aba2-4 and aba3-2. These results indicate that there are two regulatory pathways mediating the inhibitory effects of NO 3 ± in A. thaliana roots. One pathway is ABA-dependent and involves ABI4 and ABI5, whereas the second pathway is ABA-independent. In addition, ABA also plays a role in mediating the stimulation of LR elongation by local NO 3 ± applications.

Environmental nitrate signals through abscisic acid in the root tip

“…ABI4 and ABI5 expression have long been known to be induced by ABA, [56][57][58] and nitrate modulation of root architecture requires the function of both ABI4 and ABI5, but not other ABI genes. 16 Together, these observations suggest that SCR is an integral component of the ABA signaling network regulating root growth, and that ABI4 and ABI5 function downstream of nitrate in the control of root growth. Finally, the position of SCR squarely within the ABA signaling pathway indicates that ABA must stimulate expression of responsive genes ABI4 and ABI5 by inhibiting an inhibitor, SCR (Fig.…”

“…8 Root branching in response to local nitrate signals had been previously shown to require abscisic acid (ABA) signaling, but the mechanism was unknown. 16,17 Both ABA and nitrate have multiple effects on the elaboration of root architecture, so crosstalk was likely, but it could either be direct or indirect. Recent work analyzing nitrate signaling in Arabidopsis reveals a sensitive mechanism linking nitrate with ABA signaling and activation of a negative feedback loop to reduce nitrate acquisition when environmental nitrate remains high.…”

Root system architecture: insights fromArabidopsisand cereal crops

“…In addition to closure of stomata to reduce water loss by transpiration, one ABA-mediated response to drought is the elongation of the primary root; more recently, evidence is growing that ABA also regulates lateral root branching, including in normal, non-drought conditions [82]. ABA signalling appears to connect many factors known to inhibit lateral root number and elongation to the resultant phenotype: for instance, lateral root inhibition in response to homogeneously high soil nitrate [83,84] and the inhibitory effect on lateral root development observed as a result of high (sugar) carbon : nitrogen ratios in the soil [85,86].…”

Nitrate transporters: an overview in legumes

“…For example, hormones coordinate the responses modulated by external environment, regulating both primary root growth and LR initiation and development. Auxin (indole-3-acetic acid, IAA) and ABA have both been proposed to play a role in mediating nitrate effects on LR development (Signora et al 2001;De Smet et al 2006;Walch-Liu et al 2006;Zhang et al 2007). In M. truncatula, studies (summarized on Fig.…”