Dissecting the molecular basis of the regulation of wood formation by auxin in hybrid aspen
The Plant Cell: 2008 20:843-855
Indole acetic acid (auxin) is a key regulator of wood formation,and an observed overlap between auxin concentration gradientand developing secondary xylem cells has led to the hypothesisthat auxin regulates wood formation by acting as a morphogen.We dissected the role of auxin in wood formation by identifyingthe auxin-responsive transcriptome in wood-forming tissues andinvestigating alterations in wood formation in transgenic hybridaspen plants (Populus tremula x Populus tremuloides) with perturbedauxin signaling. We showed that auxin-responsive genes in wood-formingtissues respond dynamically to changes in cellular auxin levels.However, the expression patterns of most of the auxin-responsivegenes displayed limited correlation with the auxin concentrationacross this developmental zone. Perturbing auxin signaling byreducing auxin responsiveness reduced the cambial cell divisionactivity, caused spatial deregulation of cell division of thecambial initials, and led to reductions in not only radial butalso axial dimensions of fibers and vessels. We propose that,instead of acting as a morphogen, changes in auxin concentrationin developing secondary xylem cells may provide important regulatorycues that modulate the expression of a few key regulators; these,in turn, may control the global gene expression patterns thatare essential for normal secondary xylem development.
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