Biomedical subjects

Grégory Vert

Publications and source records attributed to Grégory Vert.

5 recordsLinked to original sources

PubMed2006

Downstream nuclear events in brassinosteroid signalling.

Brassinosteroids (BRs) are steroid hormones that control many aspects of plant growth and development. BRs bind to the plasma membrane receptor kinase BRI1, and act through a signalling pathway that involves a glycogen synthase kinase-3-like kinase (BIN2) and a serine/threonine phosphatase (BSU1). Previous models proposed that BIN2 negatively regulates BR signalling by controlling the stability and subcellular localization of the related transcription factors BES1 and BZR1 by phosphorylation, in a manner reminiscent of the canonical Wnt signalling pathway of metazoans. Here we present strong evidence for a different mode of regulation of BR signalling. We show that BES1 is localized constitutively to the nucleus, where its activity is modulated by nuclear-localized BIN2 kinase. BIN2-mediated phosphorylation of BES1 inhibits its DNA-binding activity on BR-responsive target promoters and its transcriptional activity through impaired multimerization. Our observations demonstrate that phosphorylation-dependent inhibition of DNA binding and trans-activation is the key primary mechanism of BES1 regulation.

Arabidopsis↗

PubMed2005

A putative function for the arabidopsis Fe-Phytosiderophore transporter homolog AtYSL2 in Fe and Zn homeostasis.

Although Arabidopsis thaliana does not produce phytosiderophores (PS) under Fe deficiency, it contains eight homologs of the metal-PS/metal-nicotianamine (NA) transporter ZmYS1 from maize. This study aimed to investigate whether one of the closest Arabidopsis homologs to ZmYS1, AtYSL2, is involved in metal-chelate transport. Northern analysis revealed high expression levels of AtYSL2 in Fe-sufficient or Fe-resupplied roots, while under Fe deficiency transcript levels decreased. Quantitative real-time polymerase chain reaction (PCR) and analysis of transgenic plants expressing an AtYSL2 promoter::beta-glucuronidase gene further allowed the detection of down-regulated AtYSL2 gene expression under Zn and Fe deficiency. In contrast to ZmYS1, AtYSL2 did not mediate metal-PS or metal-NA transport in yeast mutants defective in Cu or Fe uptake, nor did AtYSL2 mediate Fe(II)-NA-, Fe(III)-NA- or Ni(II)-NA-inducible currents when assayed by two-electrode voltage clamp in Xenopus oocytes. Moreover, truncation of the N-terminus to remove putative phosphorylation sites that might trigger autoinhibition did not confer functionality to AtYSL2. A direct growth comparison of yeast cells transformed with AtYSL2 in two different yeast expression vectors showed that transformation with empty pFL61 repressed growth even under non-limiting Fe supply. We therefore conclude that the yeast complementation assay previously employed does not allow the identification of AtYSL2 as an Fe-NA transporter. Transgenic plants expressing an AtYSL2 promoter::beta-glucuronidase gene showed expression in root endodermis and pericycle cells facing the meta-xylem tubes. Taken together, our investigations support an involvement of AtYSL2 in Fe and Zn homeostasis, although functionality or substrate specificity are likely to differ between AtYSL2 and ZmYS1.

Animals↗

PubMed2005

Molecular mechanisms of steroid hormone signaling in plants.

Brassinosteroids (BRs), the polyhydroxylated steroid hormones of plants, regulate the growth and differentiation of plants throughout their life cycle. Over the past several years, genetic and biochemical approaches have yielded great progress in understanding BR signaling. Unlike their animal counterparts, BRs are perceived at the plasma membrane by direct binding to the extracellular domain of the BRI1 receptor S/T kinase. BR perception initiates a signaling cascade, acting through a GSK3 kinase, BIN2, and the BSU1 phosphatase, which in turn modulates the phosphorylation state and stability of the nuclear transcription factors BES1 and BZR1. Microarray technology has been used extensively to provide a global view of BR genomic effects, as well as a specific set of target genes for BES1 and BZR1. These gene products thus provide a framework for how BRs regulate the growth of plants.

Arabidopsis↗

PubMed2004

Nuclear protein phosphatases with Kelch-repeat domains modulate the response to brassinosteroids in Arabidopsis.

Perception of the plant steroid hormone brassinolide (BL) by the membrane-associated receptor kinase BRI1 triggers the dephosphorylation and accumulation in the nucleus of the transcriptional modulators BES1 and BZR1. We identified bsu1-1D as a dominant suppressor of bri1 in A abidopsis. BSU1 encodes a nuclear-localized serine-threonine protein phosphatase with an N-terminal Kelch-repeat domain, and is preferentially expressed in elongating cells. BSU1 is able to modulate the phosphorylation state of BES1, counter acting the action of the glycogen synthase kinase-3 BIN2, and leading to inc eased steady-state levels of dephosphorylated BES1. BSU1 belongs to a small gene family; loss-of-function analyses unravel the extent of functional overlap among members of the family and confirm the role of these phosphatases in the control of cell elongation by BL. Our data indicate that BES1 is subject to antagonistic phosphorylation and dephosphorylation reactions in the nucleus, which fine-tune the amplitude of the response to BL.

Amino Acid Sequence↗

PubMed2002

IRT1, an Arabidopsis transporter essential for iron uptake from the soil and for plant growth.

Plants are the principal source of iron in most diets, yet iron availability often limits plant growth. In response to iron deficiency, Arabidopsis roots induce the expression of the divalent cation transporter IRT1. Here, we present genetic evidence that IRT1 is essential for the uptake of iron from the soil. An Arabidopsis knockout mutant in IRT1 is chlorotic and has a severe growth defect in soil, leading to death. This defect is rescued by the exogenous application of iron. The mutant plants do not take up iron and fail to accumulate other divalent cations in low-iron conditions. IRT1-green fluorescent protein fusion, transiently expressed in culture cells, localized to the plasma membrane. We also show, through promoter::beta-glucuronidase analysis and in situ hybridization, that IRT1 is expressed in the external cell layers of the root, specifically in response to iron starvation. These results clearly demonstrate that IRT1 is the major transporter responsible for high-affinity metal uptake under iron deficiency.

Arabidopsis↗