Hormonal and developmental regulation of two arabinogalactan-proteins in xylem of loblolly pine (Pinus taeda)

The protein cores of two arabinogalactan-proteins are preferentially expressed at very high levels in differentiating xylem of loblolly pine. Arabinogalactan-proteins are hypothesized to play important roles in xylem development, The objectives of the described research were to identify signals responsible for the regulation of PtX3H6 and PtX14A9 expression and to assess their expression during seedling development. Application of inhibitors of the phytohormones auxin, gibberellic acid, and ethylene to pine seedlings and subsequent northern blot analyses indicate that PtX3H6 expression is suppressed by inhibitors of auxin and ethylene and that PtX14A9 expression is suppressed by all 3 hormone inhibitors. PtX3H6 is first expressed in germinating embryos. Expression of PtX14A9 is not observed until several days later. In young stems, both genes are expressed more in the radially expanding hypocotyls than in elongating epicotyls with PtX14A9 having a higher ratio of hypocotyl to epicotyl expression. These results indicate that PtX3H6 and PtX14A9 are differently regulated during seedling development and that these differences may be mediated by different hormonal signaling.