Auxin regulates distal stem cell differentiation in Arabidopsis roots

Abstract

The stem cell niche in the root meristem is critical for the development of the plant root system. The plant hormone auxin acts as a versatile trigger in many developmental processes, including the regulation of root growth, but its role in the control of the stem cell activity remains largely unclear. Here we show that local auxin levels, determined by biosynthesis and intercellular transport, mediate maintenance or differentiation of distal stem cells in the Arabidopsis thaliana roots. Genetic analysis shows that auxin acts upstream of the major regulators of the stem cell activity, the homeodomain transcription factor WOX5, and the AP-2 transcription factor PLETHORA. Auxin signaling for differentiation of distal stem cells requires the transcriptional repressor IAA17/AXR3 as well as the ARF10 and ARF16 auxin response factors. ARF10 and ARF16 activities repress the WOX5 transcription and restrict it to the quiescent center, where WOX5, in turn, is needed for the activity of PLETHORA. Our investigations reveal that long-distance auxin signals act upstream of the short-range network of transcriptional factors to mediate the differentiation of distal stem cells in roots.n plants, the permanent populations of stem cells (meristems) generate growth during the entire plant's life span. The wellorganized root meristem of Arabidopsis thaliana contains a small number of mitotically inactive central cells, known as the quiescent center (QC), surrounded by different types of stem cells that can differentiate into diversified cell types in roots (1). The differentiation rate of stem cells has a direct impact on the activity of the root meristem and thus determines the root architecture. The homeobox gene WUSCHEL-RELATED HOMEOBOX 5 (WOX5) is a major regulator of the root stem cell activity. WOX5 is expressed in the QC and maintains the surrounding stem cells, as demonstrated by differentiation of distal stem cells (DSC) in the wox5 mutant and the inhibited DSC differentiation in the WOX5 overexpressors (2). The other important regulators of the root stem cell activity are the PLETHORA (PLT) AP2-domain transcription factors with PLT1 being the key member of the gene family involved in the root (3, 4). Despite the accumulated knowledge on these factors required for stem cell activity, little is known about their mutual functional relations and how they are connected to other, also long-distance, signaling networks.The plant hormone auxin is an important long-and shortdistance signal that controls multiple developmental processes (5, 6), including root patterning (7-12) and root cell division and elongation (13-15). Previous observations also suggest that auxin plays a role in regulating and maintaining stem cell identities (8,9,16), but the underlying mechanism remains unclear.Our investigations show that local auxin levels mediated by biosynthesis and transport play a critical role during the differentiation of DSC in roots. The components of auxin signaling including the IAA17/AXR3 transcriptional repressor and the ARF10 a...

ER-localized auxin transporter PIN8 regulates auxin homeostasis and male gametophyte development in Arabidopsis

“…All individual reactions were done in triplicate. Data were analysed as described before 40 . The primers used to quantify gene expression levels are provided in Supplementary Table S3.…”

Arabidopsis ribosomal proteins control vacuole trafficking and developmental programs through the regulation of lipid metabolism

“…Lugol Staining. Lugol staining of starch deposition in Arabidopsis roots was performed as described previously (67), with minor modification of the protocol. Seedlings were incubated with 1% Lugol's solution for 5 min.…”

PP2A-3 interacts with ACR4 and regulates formative cell division in the Arabidopsis root

“…2 A and B). However, because such a columella phenotype can also be explained by altered auxin distribution, levels, or response (11), the similarity between the pp2a-3 and acr4 mutants does not provide conclusive support for a genetic and/or physical interaction. This is especially relevant because PP2A-3 has been shown to play a role in auxin transport (36).…”

“…S1A). Several plant hormones and proteins that play a role in this process have been identified, and small regulatory networks have been proposed (3)(4)(5)(6)(7)(8)(9)(10)(11). However, our knowledge of the mechanisms and signaling networks mediating formative cell divisions is sparse and is largely derived from transcriptional data (12).…”