Involvement of Arabidopsis thaliana phospholipase Dζ2 in root hydrotropism through the suppression of root gravitropism

Abstract

Root hydrotropism is the phenomenon of directional root growth toward moisture under water-deficient conditions. Although physiological and genetic studies have revealed the involvement of the root cap in the sensing of moisture gradients, and those of auxin and abscisic acid (ABA) in the signal transduction for asymmetric root elongation, the overall mechanism of root hydrotropism is still unclear. We found that the promoter activity of the Arabidopsis phospholipase Dzeta2 gene (PLDzeta2) was localized to epidermal cells in the distal root elongation zone and lateral root cap cells adjacent to them, and that exogenous ABA enhanced the activity and extended its area to the entire root cap. Although pldzeta2 mutant root caps did not exhibit a morphological phenotype in either the absence or presence of exogenous ABA, the inhibitory effect of ABA on gravitropism, which was significant in wild-type roots, was not observed in pldzeta2 mutant roots. In root hydrotropism experiments, pldzeta2 mutations significantly retarded or disturbed root hydrotropic responses. A drought condition similar to that used in a hydrotropism experiment enhanced the PLDzeta2 promoter activity in the root cap, as did exogenous ABA. These results suggest that PLDzeta2 responds to drought through ABA signaling in the root cap and accelerates root hydrotropism through the suppression of root gravitropism.

Biology and Biochemistry of Plant Phospholipases

“…PLDζ 2-deficient mutants exhibited compromised root hydrotropic responses, and were not susceptible to the inhibitory effect of ABA on root gravitropism. The PLDζ 2 promoter was activated by exogenous ABA, and it was proposed that PLDζ 2 acts downstream of ABA to suppress root gravitropism during periods of water deficit (Taniguchi et al, 2010), although the complete signaling mechanism has not yet been elucidated.…”

The Art of Being Flexible: How to Escape from Shade, Salt, and Drought

“…Mutants in the C2 domain-containing a1, a3, and d isoforms showed reduced root growth and branching in salt, but not control, conditions (Bargmann et al, 2009;Hong et al, 2010). Also, the Phox-Pleckstrin Homology type PLDz2 isoform was shown to function in both hydrotropic and halotropic responses (Taniguchi et al, 2010;Galvan-Ampudia et al, 2013), most likely through modulation of the clathrin-mediated endocytosis of PIN2 (Galvan-Ampudia et al, 2013). These results are supported by the identification of clathrin H chain and clathrin-mediated endocytosis AP180, amino-terminal, homology/epsin, amino-terminal homology domain-containing protein accessory proteins as PA-binding proteins that are recruited to cellular membranes upon treatment with salt .…”

Differential expression of proteins in maize roots in response to abscisic acid and drought

“…As a result, increasing crop resistance to drought stress would be the most economical approach to improve its productivity and to reduce agricultural use of fresh water resources. To survive this adversity, land plants are equipped with various means of altering their metabolism, morphology and developmental processes (Jeong et al 2010;Shao et al 2008;Shinozaki and Yamaguchi-Shinozaki 2007;Taniguchi et al 2010). To understand the mechanisms of plants adaptation to drought, it is a crucial step to identify the key genes that can be used for engineering transgenic crops with improved drought tolerance without reducing yield or biomass.…”