Nitric Oxide Affects Rice Root Growth by Regulating Auxin Transport Under Nitrate Supply

Abstract

Nitrogen (N) is a major essential nutrient for plant growth, and rice is an important food crop globally. Although ammonium (NH4+) is the main N source for rice, nitrate (NO3-) is also absorbed and utilized. Rice responds to NO3- supply by changing root morphology. However, the mechanisms of rice root growth and formation under NO3- supply are unclear. Nitric oxide (NO) and auxin are important regulators of root growth and development under NO3- supply. How the interactions between NO and auxin in regulating root growth in response to NO3- are unknown. In this study, the levels of indole-3-acetic acid (IAA) and NO in roots, and the responses of lateral roots (LRs) and seminal roots (SRs) to NH4+ and NO3-, were investigated using wild-type (WT) rice, as well as osnia2 and ospin1b mutants. NO3- supply promoted LR formation and SR elongation. The effects of NO donor and NO inhibitor/scavenger supply on NO levels and the root morphology of WT and nia2 mutants under NH4+ or NO3- suggest that NO3--induced NO is generated by the nitrate reductase (NR) pathway rather than the NO synthase (NOS)-like pathway. IAA levels, [3H] IAA transport, and PIN gene expression in roots were enhanced under NO3- relative to NH4+ supply. These results suggest that NO3- regulates auxin transport in roots. Application of SNP under NH4+ supply, or of cPTIO under NO3- supply, resulted in auxin levels in roots similar to those under NO3- and NH4+ supply, respectively. Compared to WT, the roots of the ospin1b mutant had lower auxin levels, fewer LRs, and shorter SRs. Thus, NO affects root growth by regulating auxin transport in response to NO3-. Overall, our findings suggest that NO3- influences LR formation and SR elongation by regulating auxin transport via a mechanism involving NO.

NO and ABA Interaction Regulates Tuber Dormancy and Sprouting in Potato

“…NO is a gaseous free radical that can easily diffuse through biofilms. NO plays a role in numerous plant physiological processes (Begara-Morales et al, 2019), such as transport (Sun et al, 2018), germination (Liu et al, 2010;Arc et al, 2013a), flowering (Khurana et al, 2011), metabolism (Hasanuzzaman et al, 2018), and senescence (Sun, 2018). Moreover, NO is a significant signaling molecule that regulates the plant response to various nonbiological and biological stresses (Begara-Morales et al, 2018), such as stomatal closure (Zhang et al, 2019), heat stress (Parankusam et al, 2017), disease (Srinivas et al, 2014), drought (Wang et al, 2016), and programmed cell death (Ma et al, 2010).…”

Root Development and Stress Tolerance in rice: The Key to Improving Stress Tolerance without Yield Penalties

“…These findings indicated that MYC2 mediates JA-induced inhibition of apical root growth by directly suppressing the expression of auxin-responsive PLTs. This also suggested that auxin and its downstream regulators mediate the stress-induced inhibition of root growth, and the hypothesis is supported by an increasing number of studies [52][53][54].…”

Signalling Overlaps between Nitrate and Auxin in Regulation of The Root System Architecture: Insights from the Arabidopsis thaliana

“…Auxin stabilizes the communication among TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALLING F-BOX proteins (TIR1/AFB3) and Domain II of AUXIN/INDLOE-3-ACETIC ACID (AUX/IAA) transcriptional co-regulators to stimulates the ubiquitin-dependent breakdown of AUX/IAA protein in the 26S proteasome [111] (Figure 2B). When the auxin concentration is low, individuals from the AUXIN/IAA-INDUCIBLE (AUX/IAA) family of transcriptional repressors bind with DNA-binding protein of ARF [112,113], which exactly possess auxin-response promoter elements (AuxREs) in various auxin-regulated genes [114,115]. AUX/IAA protein inhibits the ARF function either by passively sequestering ARF protein away from their specific target promoters [116], or by interacting AUX/IAA with the co-repressor TOPLESS (TPL) to stimulate chromatin inactivation and silencing of ARF target genes [117].…”

“…Recent studies demonstrated that auxin accumulation in the LRs primordia overlaps with the low nitrate-stimulated expression of TAR2 in the root [16,85]. The application of the 2-4-carboxyphenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) under NO 3 − supply, initiates auxin (IAA) level in the root [112]. In contrast to wild-type (WT), the ospin1b mutant has lower auxin level in their root, fewer LRs and shorter seminal root (SRs).…”

“…In contrast to wild-type (WT), the ospin1b mutant has lower auxin level in their root, fewer LRs and shorter seminal root (SRs). These results demonstrate the effect of NO 3 − on LR arrangement and seminal root (SR) elongation by regulating auxin transport and NO 3 − [112]. NO 3 − and IAA regulate the expression of the rice adenosine phosphate isopentenyltransferase (OsIPT) genes, limit the cytokinin (CTKs) biosynthesis in the tiller nodes, thereby regulating the development of tiller bud in rice [17].…”