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...

Edited by Joseph M. JezField studies have shown that plants growing next to herbivore-infested plants acquire higher resistance to herbivore damage. This increased resistance is partly due to regulation of plant gene expression by volatile organic compounds (VOCs) released by plants that sense environmental challenges such as herbivores. The molecular basis for VOC sensing in plants, however, is poorly understood. Here, we report the identification of TOPLESS-like proteins (TPLs) that have VOC-binding activity and are involved in VOC sensing in tobacco. While screening for volatiles that induce stress-responsive gene expression in tobacco BY-2 cells and tobacco plants, we found that some sesquiterpenes induce the expression of stress-responsive genes. These results provided evidence that plants sense these VOCs and motivated us to analyze the mechanisms underlying volatile sensing using tobacco as a model system. Using a pulldown assay with caryophyllene derivative-linked beads, we identified TPLs as transcriptional co-repressors that bind volatile caryophyllene analogs. Overexpression of TPLs in cultured BY-2 cells or tobacco leaves reduced caryophyllene-induced gene expression, indicating that TPLs are involved in the responses to caryophyllene analogs in tobacco. We propose that unlike animals, which use membrane receptors for sensing odorants, a transcriptional co-repressor plays a role in sensing and mediating VOC signals in plant cells.For terrestrial animals, odorants or volatile organic compounds (VOCs) 5 possess important biological and ecological information such as food, predator, and species. Sensing these chemical cues, animals take appropriate behavior such as attraction or avoidance, ensuring their survival. Plants also have to acquire information from the external environment and take appropriate action for survival. Defense or stress-related genes are up-regulated upon exposure to specific VOCs to prepare for environmental change in plants (1-4). For example, defense genes are induced in healthy lima bean leaves upon exposure to VOCs from infested leaves, but not from healthy or artificially wounded leaves (5). In addition, VOCs released from infested leaves prime neighboring plants for direct and indirect defense against future herbivore attack (6). VOCs are also used as cues for host selection and location by parasitic plants (7). Several individual compounds from host plants also show attractiveness to parasitic plants. Regardless of accumulated evidence for the VOC effects in plants, a molecular basis for the VOC detection by plant cells has not been revealed.In animals, VOCs are recognized by odorant receptors in the olfactory neural system that constitutes the largest G protein-coupled receptor (GPCR) family. In contrast, plants have only a few GPCR genes that appear to have different functions (8). It has been unclear how VOCs are sensed and the information is converted to signals that induce the specific responses in plant cells at the level of receptors. It is possible that plants have a...

Anthocyanins are a chemically diverse class of secondary metabolites that color most flowers and fruits. They consist of three aromatic rings that can be substituted with hydroxyl, sugar, acyl, and methyl groups in a variety of patterns depending on the plant species. To understand how such chemical diversity evolved, we isolated and characterized METHYLATION AT THREE2 (MT2) and the two METHYLATION AT FIVE (MF) loci from Petunia spp., which direct anthocyanin methylation in petals. The proteins encoded by MT2 and the duplicated MF1 and MF2 genes and a putative grape (Vitis vinifera) homolog Anthocyanin O-Methyltransferase1 (VvAOMT1) are highly similar to and apparently evolved from caffeoyl-Coenzyme A O-methyltransferases by relatively small alterations in the active site. Transgenic experiments showed that the Petunia spp. and grape enzymes have remarkably different substrate specificities, which explains part of the structural anthocyanin diversity in both species. Most strikingly, VvAOMT1 expression resulted in the accumulation of novel anthocyanins that are normally not found in Petunia spp., revealing how alterations in the last reaction can reshuffle the pathway and affect (normally) preceding decoration steps in an unanticipated way. Our data show how variations in gene expression patterns, loss-of-function mutations, and alterations in substrate specificities all contributed to the anthocyanins' structural diversity.

It has been reported since the 1980s that plants neighboring to herbivore‐infested plants in field acquire higher levels of resistance to damages. The current understanding is that it is due to volatile organic compounds (VOCs), released from wounded plants, which trigger defensive responses in neighboring healthy plants. The molecular basis for sensing VOCs in plants, however, is poorly understood. Here, we report the identification of a transcriptional regulatory protein that has a VOC‐binding activity and is involved in VOC sensing in tobacco. Via screening for volatiles that induce stress‐responsive gene expression in tobacco BY‐2 cell and tobacco plants, we found that some sesquiterpenes, caryophyllene analogs, induced stress‐responsive gene. These results provide evidence that plants sense molecular species of VOCs, and motivated us focusing on VOC binding molecules to analyze the mechanisms underlying volatile sensing. As a result, we identified TOPLESS‐like proteins (TPLs), transcriptional co‐repressors, that were specifically bound to the caryophyllene derivative‐linked beads. Importantly, when TPLs was overexpressed in BY‐2 cell line, stress‐responsive gene expression by the caryophyllene was reduced. These results suggest that the interaction of TPLs and caryophyllene analogs lead to the induction of target genes and thus shed light on the mechanism of VOC sensing in plants.