Laplaze Laurent, Benkova Eva, Casimiro Ilda, Maes Lies, Vanneste Steffen, Swarup Ranjan, Weijers Dolf, Calvo Vanessa, Parizot Boris, Herrera-Rodriguez Maria Begoña, Offringa Remko, Graham Neil, Doumas Patrick, Friml Jiri, Bogusz Didier, Beeckman Tom, Bennett Malcolm
Institut de Recherche pour le Développement, Unité Mixte de Recherche Diversité et Adaptation des Plantes Cultivées, Agro.M, Université Montpellier 2, Equipe Rhizogenèse, France.
Plant Cell. 2007 Dec;19(12):3889-900. doi: 10.1105/tpc.107.055863. Epub 2007 Dec 7.
In Arabidopsis thaliana, lateral roots are formed from root pericycle cells adjacent to the xylem poles. Lateral root development is regulated antagonistically by the plant hormones auxin and cytokinin. While a great deal is known about how auxin promotes lateral root development, the mechanism of cytokinin repression is still unclear. Elevating cytokinin levels was observed to disrupt lateral root initiation and the regular pattern of divisions that characterizes lateral root development in Arabidopsis. To identify the stage of lateral root development that is sensitive to cytokinins, we targeted the expression of the Agrobacterium tumefaciens cytokinin biosynthesis enzyme isopentenyltransferase to either xylem-pole pericycle cells or young lateral root primordia using GAL4-GFP enhancer trap lines. Transactivation experiments revealed that xylem-pole pericycle cells are sensitive to cytokinins, whereas young lateral root primordia are not. This effect is physiologically significant because transactivation of the Arabidopsis cytokinin degrading enzyme cytokinin oxidase 1 in lateral root founder cells results in increased lateral root formation. We observed that cytokinins perturb the expression of PIN genes in lateral root founder cells and prevent the formation of an auxin gradient that is required to pattern lateral root primordia.
在拟南芥中，侧根由与木质部极相邻的根中柱鞘细胞形成。侧根发育受到植物激素生长素和细胞分裂素的拮抗调控。虽然关于生长素如何促进侧根发育已有很多了解，但细胞分裂素抑制侧根发育的机制仍不清楚。据观察，提高细胞分裂素水平会破坏拟南芥侧根起始以及作为侧根发育特征的规则分裂模式。为了确定侧根发育中对细胞分裂素敏感的阶段，我们使用GAL4-GFP增强子捕获系，将根癌农杆菌细胞分裂素生物合成酶异戊烯基转移酶的表达靶向木质部极中柱鞘细胞或幼侧根原基。反式激活实验表明，木质部极中柱鞘细胞对细胞分裂素敏感，而幼侧根原基不敏感。这种效应在生理上具有重要意义，因为在侧根起始细胞中反式激活拟南芥细胞分裂素降解酶细胞分裂素氧化酶1会导致侧根形成增加。我们观察到，细胞分裂素扰乱侧根起始细胞中PIN基因的表达，并阻止形成侧根原基模式所需的生长素梯度。
