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Accueil du site → Doctorat → Australie → 2013 → Cell type-specific transcriptional responses of plants to salinity

University of Adelaide (2013)

Cell type-specific transcriptional responses of plants to salinity

Evrard, Aurelie

Titre : Cell type-specific transcriptional responses of plants to salinity.

Auteur : Evrard, Aurelie

Université de soutenance : University of Adelaide

Grade : Doctor of Philosophy (PhD) 2013

Résumé
Soil salinity reduces the growth of glycophytic plants such as Arabidopsis thaliana and rice. In vascular plants, roots are organized into concentric layers of cells and each layer has a specific biological function coordinated with other cell types in the root. Therefore, genes differentially expressed in response to a salt stress are also likely to be changing only in specific cell types, and thus may not be revealed at the organ level. In order to identify novel salt-responsive genes, cell-type specific transcriptomic approaches were undertaken in Arabidopsis thaliana and rice, with application of physiologically reasonable salt stress (50 mM) over 48 hours. Two cell-types from the root were chosen in both species for their potential role in salt storage and transport : cortical and pericycle/stelar cells respectively. Cell-types of interest expressing specifically Green Fluorescent Protein (GFP) were isolated from the rest of the root using fluorescence-activated cell sorting (FACS). The outer layer of the root was found to be responding more than the inner part of the root after 48 hours of salt stress, with an overall down-regulation in both rice and Arabidopsis. Arabidopsis cortical cells responding to salt seem to regulate the cell wall biosynthesis, which may modulate the shape of the cells or alter the apoplastic movements of solutes in response to salt. Genes related to transport were affected by salt in Arabidopsis, with the crucial role of cortical cells in the movement of solutes being evident. Rice cortical cells respond to salt by showing a more extreme defense reaction in changing the protein metabolism and the regulation of transcription. The response of the inner part of the rice root to 48 hours of mild salt stress showed up-regulation of genes implicated in broader functional categories. The biological relevance of genes revealed using cell type-specific transcriptomics was demonstrated in a salt assay using knock-out (KO) lines of candidate genes from both cell-types in Arabidopsis thaliana. Three KO mutant lines showed 20% reduction in shoot sodium after 5 weeks of salt stress and were also able to maintain a higher shoot dry weight. These transcriptomic studies of isolated stelar and cortical cells in response to a mild salt stress have revealed salt responsive genes and pathways, indicating new areas for further study, and contributing to our understanding of the complex responses of plants to their environment at the cellular level.

Mots clés : cell type-specific ; rice ; arabidopsis ; salt ; salinity ; gene expression ; FACS ; protoplast ; RNA

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