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Gibberellins Regulate Lateral Root Formation in Populus through Interactions with Auxin and Other Hormones
Jiqing Gou a, Steven H. Strauss b, Chung Jui Tsai c, Kai Fang d, Yiru Chen a, Xiangning Jiang d and Victor B. Busov a
a School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan 49931-1295
b Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon 97331-5752
c Warnell School of Forestry and Natural Resources, Department of Genetics, University of Georgia, Athens, Georgia 30602-2152
d National Engineering Laboratory for Tree Breeding, College of Life Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, People's Republic of China
The role of gibberellins (GAs) in regulation of lateral root development is poorly understood. We show that GA-deficient (35S:PcGA2ox1) and GA-insensitive (35S:rgl1) transgenic Populus exhibited increased lateral root proliferation and elongation under in vitro and greenhouse conditions, and these effects were reversed by exogenous GA treatment. In addition, RNA interference suppression of two poplar GA 2-oxidases predominantly expressed in roots also decreased lateral root formation. GAs negatively affected lateral root formation by inhibiting lateral root primordium initiation. A whole-genome microarray analysis of root development in GA-modified transgenic plants revealed 2069 genes with significantly altered expression. The expression of 1178 genes, including genes that promote cell proliferation, growth, and cell wall loosening, corresponded to the phenotypic severity of the root traits when transgenic events with differential phenotypic expression were compared. The array data and direct hormone measurements suggested crosstalk of GA signaling with other hormone pathways, including auxin and abscisic acid. Transgenic modification of a differentially expressed gene encoding an auxin efflux carrier suggests that GA modulation of lateral root development is at least partly imparted by polar auxin transport modification. These results suggest a mechanism for GA-regulated modulation of lateral root proliferation associated with regulation of plant allometry during the stress response.