GIF Transcriptional Co-regulators Control Root Meristem Homeostasis

In the root meristem, the quiescent center (QC) is surrounded by stem cells, which in turn generate the different cell types of the root. QC cells rarely divide under normal conditions but can replenish (补充) damaged stem cells. In the proximal meristem (近端分生组织), the daughters of stem cells, which are referred to as transit amplifying cells (过渡扩充细胞), undergo additional rounds of cell division prior to differentiation. Here, we describe the functions of GRF-INTERACTING FACTORs (GIFs), including ANGUSTIFOLIA3 (AN3), in Arabidopsis thaliana roots. GIFs have been shown to interact with GRF transcription factors and SWI/SNF chromatin remodeling complexes (染色质重塑复合物). We found that combinations of GIF mutants cause the loss of QC identity. However, despite their QC impairment (损害), GIF mutants have a significantly enlarged (扩大) root meristem with additional lateral root cap (根冠) layers. We show that the increased expression of PLETHORA1 (PLT1) is at least partially responsible for the large root meristems of an3 mutants. Furthermore, we found that GIFs are necessary for maintaining the precise expression patterns of key developmental regulators and that AN3 complexes bind directly to the promoter regions of PLT1 as well as SCARECROW. We propose that AN3/GIFs participate in different pathways that control QC organization and the size of the meristem.

在根的分生组织中，静止中心QC四周由干细胞包围，而干细胞会产生根中不同细胞类型的细胞。QC细胞在正常条件下一般不分裂，但其能够补充损坏掉的干细胞。在近端分生组织中，干细胞的子代，也就是通常被称作为过渡扩充细胞的一类细胞会在分化之前经历多一轮的分裂。本文鉴定了GIFs和AN3基因在拟南芥根中的功能。GIFs可以与GRF转录因子以及SWI/SNF染色质重塑复合物进行互作。作者发现GIF突变体的不同组合会导致QC丧失其本身的特性。然而，除了QC的损坏，GIF突变体根分生组织显著扩大，还会多一层侧根冠层。本文显示an3突变体中分生组织增大部分是由于PLT1基因表达量的增加所导致的。此外，作者还发现GIFs对于关键发育调控子精确表达模式的维持至关重要，AN3复合物会直接结合到PLT1和SCARECROW基因的启动子区域。作者认为AN3/GIFs会通过参与不同的通路来控制QC特性的维持和分生组织的大小。

doi: https://doi.org/10.1105/tpc.17.00856