Root Hair-Specific EXPANSIN A7 Is Required for Root Hair Elongation in Arabidopsis

Abstract

Expansins are non-hydrolytic cell wall-loosening proteins that are involved in the cell wall modifications that underlie many plant developmental processes. Root hair growth requires the accumulation of cell wall materials and dynamic cell wall modification at the tip region. Although several lines of indirect evidence support the idea that expansin-mediated wall modification occurs during root hair growth, the involvement of these proteins remains to be demonstrated in vivo. In this study, we used RNA interference (RNAi) to examine the biological function of Arabidopsis thaliana EXPANSIN A7 (AtEXPA7), which is expressed specifically in the root hair cell. The root hairspecific AtEXPA7 promoter was used to drive RNAi expression, which targeted two independent regions in the AtEXPA7 transcript. Quantitative reverse transcriptase-PCR analyses were used to examine AtEXPA7 transcript levels. In four independent RNAi transformant lines, RNAi expression reduced AtEXPA7 transcript levels by 25-58% compared to controls. Accordingly, the root hairs of RNAi transformant lines were 25-48% shorter than control plants and exhibited a broader range of lengths than the controls. Our results provide in vivo evidence that expansins are required for root hair tip growth.

Root Hairs

“…In Arabidopsis, two members of the expansin family of cell wall proteins, EXPANSIN A7 (EXPA7: At1g12560) and EXPANSIN A18 (EXPA18: At1g62980), exhibit root-hair-specific expression (Cho and Cosgrove, 2002;Jones et al, 2006;Won et al, 2009;Bruex et al, 2012), and altering their levels by treatment with exogenous protein preparations or by RNAi-based suppression, resulted in altered root hair tip growth (Cosgrove et al, 2002;Lin et al, 2011). Many hydroxyproline-rich glycoproteins (HRGPs) are found in cell walls (Velasquez et al, 2011;Mohnen and Tierney, 2011).…”

Tracheophytes Contain Conserved Orthologs of a Basic Helix-Loop-Helix Transcription Factor That Modulate ROOT HAIR SPECIFIC Genes

“…Because EXPA7 is required for normal root hair growth in Arabidopsis (Lin et al, 2011) and its orthologs are well conserved throughout angiosperms (Kim et al, 2006), we presumed that root hair-specific orthologs of EXPA7 are involved in root hair growth in S. moellendorffii. A phylogenetic analysis showed that the S. moellendorffii genome includes two EXPAs that belong to the same clade as other EXPA7 orthologs from angiosperms (Supplemental Figure 2 and Supplemental Data Set 2).…”

Establishment of a High-efficiency Genetic Transformation System of Cucumber (Cucumis sativus) using Csexpansin 10 (CsEXP10) Gene

“…During the last three decades, cucumber transformation techniques have undergone advances. The most effective method to transfer the desired genes into the cucumber genome is to use an Agrobacterium-mediated transformation approach (Trulson et al, 1986;Kose and Koç, 2003;Lin et al, 2011a). However, the genotype dependency, lowregeneration efficiency, and low reproducibility of this transformation system limit the use of transformation techniques in the genetic improvement of cucumber.…”