RIKEN Plant Science Center, 1-7-22, Suehiro, Tsurumi, Yokohama 230-0045, Japan.
Plant J. 2012 Jan;69(2):355-65. doi: 10.1111/j.1365-313X.2011.04795.x. Epub 2011 Nov 8.
Cytokinins are phytohormones that play key roles in the maintenance of stem cell activity in plants. Although alternative single-step and two-step activation pathways for cytokinin have been proposed, the significance of the single-step pathway which is catalyzed by LONELY GUY (LOG), is not fully understood. We analyzed the metabolic flow of cytokinin activation in Arabidopsis log multiple mutants using stable isotope-labeled tracers and characterized the mutants' morphological and developmental phenotypes. In tracer experiments, cytokinin activation was inhibited most pronouncedly by log7, while the other log mutations had cumulative effects. Although sextuple or lower-order mutants did not show drastic phenotypes in vegetative growth, the log1log2log3log4log5log7log8 septuple T-DNA insertion mutant in which the LOG-dependent pathway is impaired, displayed severe retardation of shoot and root growth with defects in the maintenance of the apical meristems. Detailed observation of the mutants showed that LOG7 was required for the maintenance of shoot apical meristem size. LOG7 was also suggested to play a role for normal primary root growth together with LOG3 and LOG4. These results suggest a dominant role of the single-step activation pathway mediated by LOGs for cytokinin production, and overlapping but differentiated functions of the members of the LOG gene family in growth and development.
细胞分裂素是植物中维持干细胞活性的关键激素。虽然已经提出了细胞分裂素的替代单步和两步激活途径，但由 LONELY GUY（LOG）催化的单步途径的意义尚未完全理解。我们使用稳定同位素标记示踪剂分析了拟南芥 log 多突变体中细胞分裂素激活的代谢流，并表征了突变体的形态和发育表型。在示踪剂实验中，log7 最显著地抑制细胞分裂素的激活，而其他 log 突变具有累积效应。虽然六倍体或更低阶的突变体在营养生长中没有表现出明显的表型，但 LOG 依赖性途径受损的 log1log2log3log4log5log7log8 七倍体 T-DNA 插入突变体显示出严重的芽和根生长迟缓，顶端分生组织维持缺陷。对突变体的详细观察表明，LOG7 对于维持芽顶端分生组织的大小是必需的。LOG7 还与 LOG3 和 LOG4 一起，为正常的主根生长发挥作用。这些结果表明，由 LOG 介导的单步激活途径在细胞分裂素产生中起主导作用，并且 LOG 基因家族成员在生长和发育中具有重叠但不同的功能。
