The Arabidopsis NRT1/PTR FAMILY Protein NPF7.3/NRT1.5 is an Indole-3-butyric Acid Transporter Involved in Root Gravitropism

Abstract

17Active membrane transport of plant hormones and their related compounds is an essential process 18 that determines the distribution of the compounds within plant tissues and, hence, regulates various 19 physiological events. Here, we report that the Arabidopsis NITRATE TRANSPORTER 1/PEPTIDE 20 TRANSPORTER FAMILY 7.3 (NPF7.3) protein functions as a transporter of indole-3-butyric acid 21 (IBA), a precursor of the major endogenous auxin indole-3-acetic acid (IAA). When expressed in 22Auxin is the best-characterized mobile plant hormone that plays crucial roles in many 41 aspects of plant growth and development by mainly regulating cell division, cell elongation and cell 42 differentiation 1 . Indole-3-acetic acid (IAA) is the major naturally occurring auxin. Measurements of 43 IAA by mass spectrometry as well as visualization of auxin responses by reporter genes have 44 suggested that IAA is differentially distributed within plant tissues. Furthermore, appropriate IAA 45 gradients or local IAA maxima/minima are required for proper auxin functions. In fact, mutants 46 impaired in IAA transport have been isolated based on their defects in organ development and 47 (also called as CHL1 or NRT1.1) is a well-characterized dual-affinity nitrate transporter that 65 mediates nitrogen uptake from the rhizosphere, however, the same protein also transports IAA 17,18 . 66More recently, the Arabidopsis NPF5.12 protein, also named TRANSPORTER OF IBA1 (TOB1), 67 was identified as an IBA transporter that localizes to the vacuolar membrane 14 . Here, we report that 68 NPF7.3, originally identified as a low-affinity nitrate transporter (NRT1.5) and later shown to be a 69 proton/potassium antiporter in Arabidopsis 19,20 , functions as an IBA transporter. We found that 70 npf7.3 mutant roots were not able to respond properly to gravity. Our transport assays in yeast 71 demonstrated that NPF7.3 efficiently mediated IBA uptake into the cells. Asymmetric distribution of 72 auxin activities in root tips following the reorientation of roots was not observed in the npf7.3 73 mutants, and the defect was restored by IAA but not by IBA treatment. These results suggest that 74 cellular IBA uptake mediated by NPF7.3 contributes to the production of IAA required to fully 75 induce Arabidopsis root gravitropism. 76 77 78Results 79 Mutants defective in NPF7.3 exhibit altered root gravitropism 80Some of the 53 members of the Arabidopsis NPF proteins transport plant hormones such as IAA, 81 abscisic acid (ABA), gibberellin (GA) and jasmonates (jasmonoyl isoleucine; JA-Ile) 16 . Thus, we 82 compound is considered to be an IAA precursor 25,26 . Interestingly, IBA also accumulated at a much 126 higher level in the cells expressing NPF7.3 compared to the control cells (Fig. 2b). Moreover, IBA 127 was more efficiently taken into the cells expressing NPF7.3 than IAA. 128Kinetic analyses indicated that the Km values of NPF7.3 for IAA and IBA were 129 comparable (14 µM and 11 µM for IAA and IBA, respectively), however, NPF7.3 had a much higher 130Vmax va...

NPF transporters in synaptic-like vesicles control delivery of iron and copper to seeds

“…Their homologs in plants were initially characterized as nitrate or peptide transporters ( 18 ). However, in recent years, some other substrates of them were also found, namely, glucosinolates, auxin, abscisic acid, jasmonates, and gibberellins ( 20 , 21 , 26 , 36 , 37 ). Here, we identified NA as a previous unidentified substrate of the NPF family.…”

HOMEOBOX PROTEIN 24 mediates the conversion of indole‐3‐butyric acid to indole‐3‐acetic acid to promote root hair elongation

“…Therefore, it was speculated that in roots, HB24 had a distinct role in root hair elongation. Bioinformatics predicted that the expression of HB24 was greater in hair cells (H cells) compared with nonhair cells (N cells) of the root epidermis (eFP Browser, bar.utoronto.ca/efp/cgi‐bin/efpWeb.cgi) (Winter et al ., 2007; Watanabe et al ., 2020). To confirm this difference, the fluorescence signal in transgenic seedlings expressing HB24‐GFP driven by the native promoter was observed.…”

Nutrient–hormone relations: Driving root plasticity in plants

“…An unexpected aspect in nutrient-regulated hormone transport is a number of originally annotated NO À 3 and K + transporters that have been proven to also facilitate the transport of specific hormones (Figure 1B). These include NPF6.3/NRT1.1, TRH1/KUP4, and KUP9 for auxin (Vicente-Agullo et al, 2004;Krouk et al, 2010;Zhang et al, 2020); NPF5.12/TOB1 and NPF7.3/NRT1.5 for indole-3-butyric acid (IBA) (Michniewicz et al, 2019;Watanabe et al, 2020); NPF4.1/AIT3, NPF4.2/AIT4, NPF4.5/AIT2, and NPF4.6/AIT1 for ABA (Kanno et al, 2012); NPF3.1 and NPF2.10/ GTR1 for GA (Saito et al, 2015;Tal et al, 2016); and NPF2.10/ GTR1 for JA-Ile (Saito et al, 2015). All these NPF-and KUP-type transporters appear to be responsible for short-distance membrane transport of hormones and their local distribution.…”