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A WUSCHEL-Independent Stem Cell Specification Pathway Is Repressed by PHB, PHV and CNA in Arabidopsis.

ABSTRACT: The homeostatic maintenance of stem cells that carry out continuous organogenesis at the shoot meristem is crucial for plant development. Key known factors act to signal between the stem cells and an underlying group of cells thought to act as the stem cell niche. In Arabidopsis thaliana the homeodomain transcription factor WUSCHEL (WUS) is essential for stem cell initiation and maintenance at shoot and flower meristems. Recent data suggest that the WUS protein may move from the niche cells directly into the stem cells to maintain stem cell identity. Here we provide evidence for a second, previously unknown, pathway for stem cell specification at shoot and flower meristems that bypasses the requirement for WUS. We demonstrate that this novel stem cell specification pathway is normally repressed by the activity of the HD-zip III transcription factors PHABULOSA (PHB), PHAVOLUTA (PHV) and CORONA (CNA). When de-repressed, this second stem cell pathway leads to an accumulation of stem cells and an enlargement of the stem cell niche. When de-repressed in a wus mutant background, this second stem cell pathway leads to functional meristems with largely normal cell layering and meristem morphology, activation of WUS cis regulatory elements, and extensive, but not indeterminate, organogenesis. Thus, WUS is largely dispensable for stem cell specification and meristem function, suggesting a set of key stem cell specification factors, competitively regulated by WUS and PHB/PHV/CNA, remain unidentified.

SUBMITTER: Lee C

PROVIDER: S-EPMC4444308 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Publications

A WUSCHEL-Independent Stem Cell Specification Pathway Is Repressed by PHB, PHV and CNA in Arabidopsis.

Lee Chunghee C Clark Steven E SE

PloS one 20150526 5

The homeostatic maintenance of stem cells that carry out continuous organogenesis at the shoot meristem is crucial for plant development. Key known factors act to signal between the stem cells and an underlying group of cells thought to act as the stem cell niche. In Arabidopsis thaliana the homeodomain transcription factor WUSCHEL (WUS) is essential for stem cell initiation and maintenance at shoot and flower meristems. Recent data suggest that the WUS protein may move from the niche cells dire ...[more]

PMID: 26011610

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Project description:The class III HD-ZIP transcription factors regulate vascular patterning in Arabidopsis thaliana roots. In this expression study we compare the expression profile of the cna-2 phb-13 phv-11 and cna-2 phb-13 phv-11 rev-6 mutants to their wild type. The results are presented in PHABULOSA mediates an auxin signaling loop to regulate vascular patterning in Arabidopsis by Christina Joy Müller, Ana Elisa Valdés, Guodong Wang, Prashanth Ramachandran, Lisa Beste, Daniel Uddenberg, and Annelie Carlsbecker, accepted for publication in Plant Physiology Nov. 2015. Plant vascular tissues, xylem and phloem, differentiate in distinct patterns from procambial cells as an integral transport system for water, sugars and signaling molecules. Procambium formation is promoted by high auxin levels activating class III homeodomain leucine zipper (HD-ZIP III) transcription factors (TFs). In the root of Arabidopsis thaliana, HD-ZIP III TFs dose-dependently govern the patterning of the xylem axis, with higher levels promoting metaxylem cell identity in the central axis and lower levels protoxylem at its flanks. It is, however, unclear by what mechanisms the HD-ZIP III TFs control xylem axis patterning. Here we present data suggesting that an important mechanism is their ability to moderate auxin response. We found that changes in HD-ZIP III TF levels affect the expression of genes encoding core auxin response molecules. We show that one of the HD-ZIP III TFs, PHABULOSA, directly binds the promoter of both MONOPTEROS/AUXIN RESPONSE FACTOR5 (MP/ARF5), a key factor in vascular formation, and IAA20, encoding an AUX/IAA protein which is stable in the presence of auxin and able to interact with and repress MP activity. The double mutant of IAA20 and its closest homologue IAA30 forms ectopic protoxylem, while overexpression of IAA30 causes discontinuous protoxylem and occasional ectopic metaxylem, similar to a weak loss-of-function mp-mutant. Our results provide evidence that HD-ZIP III TFs directly affect auxin response and mediate a feed forward loop formed by MP and IAA20 that may focus and stabilize auxin response during vascular patterning and differentiation of xylem cell types.

Dataset Information

A WUSCHEL-Independent Stem Cell Specification Pathway Is Repressed by PHB, PHV and CNA in Arabidopsis.

Publications

A WUSCHEL-Independent Stem Cell Specification Pathway Is Repressed by PHB, PHV and CNA in Arabidopsis.

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