Department of Molecular and Cell Biology, School of Life Science and Technology, Tongji University, Shanghai, China.
Ann Bot. 2012 Jul;110(1):1-10. doi: 10.1093/aob/mcs019. Epub 2012 Feb 14.
LATERAL ORGAN BOUNDARIES DOMAIN 29 (LBD29), an important molecule downstream of auxin response factors ARF7 and ARF19, has a critical role in lateral root formation in Arabidopsis thaliana. The cell cycle activation of pericycle cells and their specification triggered by auxin are crucial for the initiation of lateral roots. In this study, we attempted to determine whether LBD29 is involved in auxin signalling and/or cell cycle regulation and to characterize the roles of LBD29 in these processes.
The impact of LBD29 on cell cycling progression in pericycle cells was investigated in lbd29 loss-of-function mutant or LBD29-over-expressing plants. The cell cycle was determined by measuring the expression of some cell cycle-related genes using in situ hybridization and quantitative real-time reverse transcription-PCR (qRT-PCR). Furthermore, the cell division in the root explants from either the lbd29 mutant, LBD29-over-expressing plants or the wild type grown in auxin-rich media was also analysed and compared by the distribution of DR5:β-glucuronidase (GUS) in the primordia or by the expression of PIN-FORMED (PIN) members and PLETHROA 1 (PLT1) which represented the auxin response by the pericycle cells.
lbd29 mutation resulted in reduced numbers of lateral roots and primordia, whereas LBD29 over-expression resulted in more lateral root and primordia formation than in the wild type. More importantly, the level of LBD29 expression was found to be positively correlated with the level of expression of cell cycle-related genes and correlated with the numbers of subcellular organelles found in pericycle cells in the maturation zone. In addition, an in vitro experiment using root explants demonstrated that the presence of LBD29 was required for the maintenance of the cell division capacity of the pericycle. Furthermore, LBD29 appeared to modify PIN-dependent auxin signalling in the primordia since there was a correlated association between the expression of PINs, PLT1 and DR5:GUS and the expression of LBD29.
The ability of LBD29 to regulate lateral root initiation is associated with its maintenance of the cell division capacity of the pericycle in response to auxin and its involvement in the auxin signalling pathway.
生长素响应因子 ARF7 和 ARF19 下游的重要分子侧向器官边界域 29（LBD29），在拟南芥侧根形成中起关键作用。生长素诱导的中柱鞘细胞的细胞周期激活和特化对于侧根的起始至关重要。在这项研究中，我们试图确定 LBD29 是否参与生长素信号转导和/或细胞周期调控，并表征 LBD29 在这些过程中的作用。
在 lbd29 功能丧失突变体或 LBD29 过表达植株中，研究 LBD29 对中柱鞘细胞细胞周期进程的影响。通过原位杂交和定量实时逆转录-PCR（qRT-PCR）测量一些细胞周期相关基因的表达来确定细胞周期。此外，还通过分析在富含生长素的培养基中生长的 lbd29 突变体、LBD29 过表达植株或野生型的根外植体中的细胞分裂，并通过观察原基中 DR5:β-葡萄糖醛酸酶（GUS）的分布或通过中柱鞘细胞的生长素反应代表物 PIN 形成（PIN）成员和 PLETHROA 1（PLT1）的表达来进行比较。
lbd29 突变导致侧根和原基数量减少，而 LBD29 过表达导致比野生型更多的侧根和原基形成。更重要的是，LBD29 的表达水平与细胞周期相关基因的表达水平呈正相关，并与成熟区中柱鞘细胞中细胞器的数量相关。此外，根外植体的体外实验表明，LBD29 的存在对于维持中柱鞘的细胞分裂能力是必需的。此外，LBD29 似乎改变了原基中依赖 PIN 的生长素信号，因为 PINs、PLT1 和 DR5:GUS 的表达与 LBD29 的表达之间存在相关关系。
LBD29 调节侧根起始的能力与其维持生长素应答的中柱鞘细胞的细胞分裂能力以及其参与生长素信号通路有关。
