摘要
Dear Editor,Seed germination is a major developmental transition in a plant＇s life that involves the concerted action of several genetic and physiological pathways （Holdsworth et al., 2008）, and mostly consists of the resumption of embryo growth after a long quiescence imposed during seed maturation. In mature seeds, germination is repressed by abscisic acid （ABA）, while favorable environmental conditions promote gibberellin （GA） biosynthesis and decrease ABA （Holdsworth et al., 2008）. The increase in GA levels is essential for the rupture of testa and endosperm （Lee et al., 2002）. The activation of cell division in the embryo is an integral part of germination that precedes the protrusion of the root through the seed coat. In Arabidopsis, this activation has been linked to significant early changes in the expression of cell-cycle elements （Masubelele et al., 2005）. In the root apical meristem （RAM）, GAs regulate cell divisions （Achard et al., 2009; 0beda-Tomás et al., 2009）. Similarly, the transcription factors （TFs） TEOSINTE BRANCHED1/ CYCLOIDEA/PROLIFERATING CELL FACTOR14 （TCP14） and TCP15 have been proposed to regulate cell proliferation （Kieffer et al., 2011）. Moreover, the activity of TCP14 is necessary to undergo seed germination and, remarkably, seeds lacking this activity are hypersensitive to the negative effects on germination of GA biosynthesis inhibitor paclobutrazol, suggesting a functional relationship between this TF and GAs （Tatematsu et al., 2008）. Taking these observations into account, we hypothesized that TCP14 and TCP15 mediate GA-dependent activation of the cell cycle during germination.
Dear Editor,Seed germination is a major developmental transition in a plant＇s life that involves the concerted action of several genetic and physiological pathways （Holdsworth et al., 2008）, and mostly consists of the resumption of embryo growth after a long quiescence imposed during seed maturation. In mature seeds, germination is repressed by abscisic acid （ABA）, while favorable environmental conditions promote gibberellin （GA） biosynthesis and decrease ABA （Holdsworth et al., 2008）. The increase in GA levels is essential for the rupture of testa and endosperm （Lee et al., 2002）. The activation of cell division in the embryo is an integral part of germination that precedes the protrusion of the root through the seed coat. In Arabidopsis, this activation has been linked to significant early changes in the expression of cell-cycle elements （Masubelele et al., 2005）. In the root apical meristem （RAM）, GAs regulate cell divisions （Achard et al., 2009; 0beda-Tomás et al., 2009）. Similarly, the transcription factors （TFs） TEOSINTE BRANCHED1/ CYCLOIDEA/PROLIFERATING CELL FACTOR14 （TCP14） and TCP15 have been proposed to regulate cell proliferation （Kieffer et al., 2011）. Moreover, the activity of TCP14 is necessary to undergo seed germination and, remarkably, seeds lacking this activity are hypersensitive to the negative effects on germination of GA biosynthesis inhibitor paclobutrazol, suggesting a functional relationship between this TF and GAs （Tatematsu et al., 2008）. Taking these observations into account, we hypothesized that TCP14 and TCP15 mediate GA-dependent activation of the cell cycle during germination.
