WVD2 and WDL1 Modulate Helical Organ Growth and Anisotropic Cell Expansion in Arabidopsis  

Abstract

Wild-type Arabidopsis roots develop a wavy pattern of growth on tilted agar surfaces. For many Arabidopsis ecotypes, roots also grow askew on such surfaces, typically slanting to the right of the gravity vector. We identified a mutant, wvd2-1, that displays suppressed root waving and leftward root slanting under these conditions. These phenotypes arise from transcriptional activation of the novel WAVE-DAMPENED2 (WVD2) gene by the cauliflower mosaic virus 35S promoter in mutant plants. Seedlings overexpressing WVD2 exhibit constitutive right-handed helical growth in both roots and etiolated hypocotyls, whereas the petioles of WVD2-overexpressing rosette leaves exhibit left-handed twisting. Moreover, the anisotropic expansion of cells is impaired, resulting in the formation of shorter and stockier organs. In roots, the phenotype is accompanied by a change in the arrangement of cortical microtubules within peripheral cap cells and cells at the basal end of the elongation zone. WVD2 transcripts are detectable by reverse transcriptase-polymerase chain reaction in multiple organs of wild-type plants. Its predicted gene product contains a conserved region named "KLEEK," which is found only in plant proteins. The Arabidopsis genome possesses seven other genes predicted to encode KLEEK-containing products. Overexpression of one of these genes, WVD2-LIKE 1, which encodes a protein with regions of similarity to WVD2 extending beyond the KLEEK domain, results in phenotypes that are highly similar to wvd2-1. Silencing of WVD2 and its paralogs results in enhanced root skewing in the wild-type direction. Our observations suggest that at least two members of this gene family may modulate both rotational polarity and anisotropic cell expansion during organ growth.The primary roots of Arabidopsis possess an intrinsic handedness to their growth, consistently forming counterclockwise coils as they elongate upon a horizontal surface of hard agar (Mirza, 1987). However, when the surface is positioned vertically, the downward growth behavior of roots dictated by gravitropism conflicts with this counterclockwise coiling tendency, resulting in a net direction of growth that is to the right of the gravity vector. It should be noted that, in this report, we follow the convention used in Simmons et al. (1995) and Rutherford and Masson (1996) to describe the direction of root coiling (clockwise or counterclockwise) and slanting (skewing: leftward or rightward of the vertical axis), as viewed through the agar medium.While slanting on vertical surfaces, root tips of wild-type Arabidopsis seedlings also exhibit a largely left-handed rotation around the net axis of growth, resulting in a moderate, left-handed twisting of the discrete cell files that make up the root epidermal layer. This left-handed preference in root tip rotation is associated with and may be responsible for the counterclockwise bias in root coiling and, by extension, rightward root slanting on vertical surfaces (Simmons et al., 1995; Rutherford and Masson, 1996). Most mu...

Arabidopsis MICROTUBULE DESTABILIZING PROTEIN40 Is Involved in Brassinosteroid Regulation of Hypocotyl Elongation

“…MDP40 belongs to a TPX2 (targeting protein for Xklp2) protein family and shares high amino acid identity with WDL7, which is a member of the microtubule-associated protein WVD2/WDL family in Arabidopsis (Yuen et al, 2003;Perrin et al, 2007). In this study, we demonstrated that MDP40 is a BZR1 target gene and that MDP40 participates in BR-mediated hypocotyl cell elongation by destabilizing cortical microtubules.…”

“…For example, the microtubule regulatory protein WAVE-DAMPENED2-LIKE3 (WDL3) is a potential BZR1 target gene. The expression levels of WDL3 are increased over 56-fold in bzr1-1D bri1-116 but are reduced by ;0.19-fold in bri1-116, suggesting a positive role in BR-mediated plant growth (Yuen et al, 2003;Sun et al, 2010). Although the physiological contributions to the BR responses have not been evaluated through genetic and physiological analyses, the results in this study demonstrate that regulation of microtubules is crucial in BR-mediated plant growth.…”

“…At1g23060 is a putative BZR1 target gene and encodes a protein that shares a ;31% amino acid identity (calculated by DNAman version 5.22) with a potential microtubule-associated protein WAVE-DAMPENED2-LIKE7 (WDL7), suggesting that this protein has a likely role in BR-mediated cell morphogenesis by regulating microtubules (Yuen et al, 2003;Perrin et al, 2007;Sun et al, 2010).…”

Loss-of-Function Mutations of ROOT HAIR DEFECTIVE3 Suppress Root Waving, Skewing, and Epidermal Cell File Rotation in Arabidopsis

“…First, most CFR-and root-skewing mutants have defects in microtubule organization and/or turnover dynamics. For example, the spr1/sku6, spr2, and wvd2-1 mutants, which show right-handed CFR and skew to the left on hard-agar surfaces, display left-handed cortical microtubule arrays in CEZ epidermal cells (Furutani et al, 2000;Yuen et al, 2003). These mutations affect various microtubule-interacting proteins (Buschmann et al, 2004;Nakajima et al, 2004;Sedbrook et al, 2004).…”

Analysis of the SHP2 enhancer for the use of tissue specific activation tagging in Arabidopsis thaliana

“…In some cases, the mutant displays a phenotype that can either be directly associated with the gene function of the activated gene (Zubko et al, 2002) or may provide an indication of the pathway in which the gene is involved (Kardailsky et al, 1999;Zhao et al, 2001;Yuen et al, 2003). The activation tagging method has also been used as a novel approach to isolate suppressor mutants of known mutant phenotypes (Neff et al, 1999;van der Graaff et al, 2003).…”