Tamaki Takayuki, Oya Satoyo, Naito Makiko, Ozawa Yasuko, Furuya Tomoyuki, Saito Masato, Sato Mayuko, Wakazaki Mayumi, Toyooka Kiminori, Fukuda Hiroo, Helariutta Ykä, Kondo Yuki
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033, Japan.
Department of Biology, Graduate School of Science, Kobe University, Kobe, 657-8501, Japan.
Commun Biol. 2020 Apr 22;3(1):184. doi: 10.1038/s42003-020-0907-3.
The phloem transports photosynthetic assimilates and signalling molecules. It mainly consists of sieve elements (SEs), which act as "highways" for transport, and companion cells (CCs), which serve as "gates" to load/unload cargos. Though SEs and CCs function together, it remains unknown what determines the ratio of SE/CC in the phloem. Here we develop a new culture system for CC differentiation in Arabidopsis named VISUAL-CC, which almost mimics the process of the SE-CC complex formation. Comparative expression analysis in VISUAL-CC reveals that SE and CC differentiation tends to show negative correlation, while total phloem differentiation is unchanged. This varying SE/CC ratio is largely dependent on GSK3 kinase activity. Indeed, gsk3 hextuple mutants possess many more SEs and fewer CCs, whereas gsk3 gain-of-function mutants partially increase the CC number. Taken together, GSK3 activity appears to function as a cell-fate switch in the phloem, thereby balancing the SE/CC ratio.
韧皮部负责运输光合产物和信号分子。它主要由作为运输“通道”的筛管分子（SEs）和作为装载/卸载货物“闸门”的伴胞（CCs）组成。尽管筛管分子和伴胞协同发挥作用，但韧皮部中决定筛管分子/伴胞比例的因素仍不清楚。在此，我们开发了一种用于拟南芥伴胞分化的新型培养系统，称为VISUAL-CC，它几乎模拟了筛管分子-伴胞复合体的形成过程。在VISUAL-CC中的比较表达分析表明，筛管分子和伴胞的分化倾向于呈负相关，而韧皮部的总分化保持不变。这种变化的筛管分子/伴胞比例在很大程度上取决于GSK3激酶活性。实际上，gsk3六重突变体拥有更多的筛管分子和更少的伴胞，而gsk3功能获得型突变体则部分增加了伴胞数量。综上所述，GSK3活性似乎在韧皮部中充当细胞命运开关，从而平衡筛管分子/伴胞比例。
