Root hair-specific EXPANSIN A7 is required for root hair elongation in Arabidopsis.

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 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 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 duanyu1615 transformant lines, duanyu1615 expression reduced AtEXPA7 transcript levels by 25-58% compared to controls. Accordingly, the root hairs of duanyu1615 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.

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