2 GENES ENCODING EXTENSIN-LIKE PROTEINS ARE PREDOMINANTLY EXPRESSED IN TOMATO ROOT HAIR-CELLS

A differential screen of a tomato root hair cDNA library resulted in t he cloning of two cDNAs, Dif10 and Dif54, whose corresponding genes ar e preferentially expressed in root hair cells as determined by analysi s of mRNA levels in various tomato organs. Transcript levels showed no increase in leaves subjected to hormonal and environmental stress tre atments. Sequence analysis of the cDNAs revealed high similarity to me mbers of the extensin family. Extensins are hydroxyproline-rich glycop roteins (HRGPs) located in the cell wall. In order to study the functi onal significance of HRGPs in root hairs, tomato seedling roots were t reated with micromolar concentrations of 3,4-dehydro-L-proline (Dhp), a selective inhibitor of prolyl hydroxylase. Dhp treatment resulted in changes in root growth and the development of root hairs with reduced hair length, suggesting an important role of HRGPs in hair morphogene sis.