Fig. 5.

Auxin methylation in the endodermis is sufficient to ensure gravitropic reorientation. (A) Endodermal expression of IAMT1 is able to recover the iamt1-1 gravitropic response. Gravitropic reorientation of iamt1-1 mutant complemented with cell-specific expression of IAMT1 in endodermis (pSCR) and epidermis (pML1). The experiments were carried out as described in Materials and Methods. Error bars represent SD. (B) Model for the role of auxin methylation on gravitropic reorientation. IAMT1 is necessary to maintain relatively low levels of auxin in the responding tissue; in the absence of such mechanism, auxin levels locally increase and enhance the PAT-mediated feedforward loop that causes auxin hyperaccumulation. The relevance of this feedforward loop is highlighted by the rescue of the iamt1 mutant phenotype by NPA.