Auxin and Ethylene Response Interactions during Arabidopsis Root Hair Development Dissected by Auxin Influx Modulators

Abstract

The plant hormones auxin and ethylene have been shown to play important roles during root hair development. However, cross talk between auxin and ethylene makes it difficult to understand the independent role of either hormone. To dissect their respective roles, we examined the effects of two compounds, chromosaponin I (CSI) and 1-naphthoxyacetic acid (1-NOA), on the root hair developmental process in wild-type Arabidopsis, ethylene-insensitive mutant ein2-1, and auxin influx mutants aux1-7, aux1-22, and double mutant aux1-7 ein2. ␤-Glucuronidase (GUS) expression analysis in the BA-GUS transgenic line, consisting of auxin-responsive domains of PS-IAA4/5 promoter and GUS reporter, revealed that 1-NOA and CSI act as auxin uptake inhibitors in Arabidopsis roots. The frequency of root hairs in ein2-1 roots was greatly reduced in the presence of CSI or 1-NOA, suggesting that endogenous auxin plays a critical role for the root hair initiation in the absence of an ethylene response. All of these mutants showed a reduction in root hair length, however, the root hair length could be restored with a variable concentration of 1-naphthaleneacetic acid (NAA). NAA (10 nm) restored the root hair length of aux1 mutants to wild-type level, whereas 100 nm NAA was needed for ein2-1 and aux1-7 ein2 mutants. Our results suggest that insensitivity in ethylene response affects the auxin-driven root hair elongation. CSI exhibited a similar effect to 1-NOA, reducing root hair growth and the number of root hair-bearing cells in wild-type and ein2-1 roots, while stimulating these traits in aux1-7and aux1-7ein2 roots, confirming that CSI is a unique modulator of AUX1.Root hairs are tip-growing, tubular-shaped outgrowths that help to anchor roots, interact with soil microorganisms, and assist in the uptake of water and nutrients (Cutter, 1978). The relatively simple and invariant cellular organization of the primary roots of Arabidopsis and the ease of isolation and characterization of mutants make it a very attractive material for studying the root hair developmental process. The first committed step for root hair development is epidermal cell specification. In many species, including Arabidopsis, the root epidermis consists of two epidermal cell types, root hair-forming trichoblast cells and hairless atrichoblast cells (Cormack, 1947(Cormack, , 1949Bunning, 1951;Cutter, 1978). Within the Arabidopsis root epidermis, cells adopt distinct fates in a position-dependent manner. Epidermal cells that overlay the junction between two cortical cell files adopt a root hair cell fate, whereas the epidermal cells that contact only one cortical cell file become hairless cells (Dolan et al., 1994;Galway et al., 1994; Berger et al., 1998).Once the immature epidermal cell adopts a root hair cell fate, it goes through characteristic changes in its shape and size (Schiefelbein, 2000). Genetic analysis revealed that the root hair initiation mutations axr2 ), axr3 (Leyser et al., 1996, and ctr1 (Kieber et al., 1993) exhibit changes in their response to two i...

MDR‐like ABC transporter AtPGP4 is involved in auxin‐mediated lateral root and root hair development

“…It has been shown that growth in the presence of either auxin or auxin transport inhibitors results in enhanced root hair length [21,22]. Here we report that exogenous IAA stimulated RH elongation in wt and atpgp4 seedlings (Fig.…”

“…in length Like for LRs, RH initiation and elongation is well known to be regulated by auxin [22]. The growth defect of LRs in the atpgp4 mutants thus prompted us to investigate RH number and lengths in atpgp4.…”

“…Genetic and physiological evidences implicate that auxin cross talks with ethylene in promoting root hair elongation [21,22]. In order to dissect the nature of this effect, and in order to test an involvement of AtPGP4 in growth defects caused by an individual plant hormone we repeated root hair measurements in the presence either of ethylene precursor aminocyclopropane carboxylic acid (ACC) which induces ectopic root hair formation or ethylene biosynthesis inhibitor aminovinylglycine (AVG) which abolishes root hairs, respectively [21].…”

“…Genetic and physiological evidence suggests that auxin is required at several specific developmental stages to facilitate root hair (RH) development and lateral root (LR) formation [16,22,23,25]. While an interpretation for root hair development is complicated by interaction among hormone response pathways [21], a shoot-derived auxin pulse has been suggested to promote the emergence of LR primordia [17].…”

The E3 ubiquitin ligase HOS1 is involved in ethylene regulation of leaf expansion inArabidopsis

“…27 In addition, this study provides evidence that HOS1 also plays a role in ethylene regulation of leaf expansion. Given that auxin and ethylene signaling is elaborately intertwined, [32][33][34] HOS1 might establish an important crosstalk. Auxin biosynthesis and ethylene signaling would be coordinated to fine-tune HOS1-mediated developmental processes.…”