Auxin and Strigolactone Signaling Are Required for Modulation of Arabidopsis Shoot Branching by Nitrogen Supply    

Abstract

The degree of shoot branching is strongly affected by environmental conditions, such as nutrient availability. Here we demonstrate that nitrate limitation reduces shoot branching in Arabidopsis (Arabidopsis thaliana) both by delaying axillary bud activation and by attenuating the basipetal sequence of bud activation that is triggered following floral transition. Ammonium supply has similar effects, suggesting that they are caused by plant nitrogen (N) status, rather than direct nitrate signaling. We identify increased auxin export from active shoot apices, resulting in increased auxin in the polar auxin transport stream of the main stem, as a likely cause for the suppression of basal branches. Consistent with this idea, in the auxin response mutant axr1 and the strigolactone biosynthesis mutant more axillary growth1, increased retention of basal branches on low N is associated with a failure to increase auxin in the main stem. The complex interactions between the hormones that regulate branching make it difficult to rule out other mechanisms of N action, such as up-regulation of strigolactone synthesis. However, the proposed increase in auxin export from active buds can also explain how reduced shoot branching is achieved without compromising root growth, leading to the characteristic shift in relative biomass allocation to the root when N is limiting.

Auxin Produced by the Indole-3-Pyruvic Acid Pathway Regulates Development and Gemmae Dormancy in the Liverwort Marchantia polymorpha

“…Similarly, apical dominance in vascular plants is believed to be positively regulated by auxin transport from the source in the apical region of the shoot. This auxin transport signal has been postulated to inhibit bud growth by regulating cytokinin and strigolactone synthesis pathways Skoog, 1933, 1934;Nordström et al, 2004;Tanaka et al, 2006;Hayward et al, 2009;de Jong et al, 2014;reviewed in Müller and Leyser, 2011). Apical dominance has also been observed in basal lineages of land plants such as liverworts, and here also, an apical auxin source is believed to be responsible for the apical dominance of shoots during thallus growth (Maravolo, 1976).…”

Regulation of Strigolactone Biosynthesis by Gibberellin Signaling

“…Because SLs are known to be involved in the regulation of diverse physiological phenomena, including shoot branching, root development, and leaf senescence, they are thought to be involved in physiological interactions with various hormones and environmental cues (Crawford et al, 2010;Dun et al, 2012;Kapulnik et al, 2011;Ha et al, 2014;de Jong et al, 2014;Mayzlish-Gati et al, 2012;Tsuchiya et al, 2010). However, the physiological cross talk between SL and GA has not been determined, despite their molecular interaction, in which the putative SL receptor, D14, interacts with the GA signaling repressor, SLR1 (Nakamura et al, 2013).…”

Environmental nitrate signals through abscisic acid in the root tip

“…[1][2][3][4][5] For plants that do not form a nitrogenfixing symbiosis, nitrate is a major source of nitrogen nutrition, and thus nitrate sensing and response is a core signaling module that intersects with many hormone signaling pathways, especially that of auxin, cytokinin and gibberellin. 6,7 More recently, the intersection of nitrate signaling with abscisic acid signaling has begun to be resolved.…”