Dissecting the molecular mechanism of Casparian strip and endodermal development in Arabidopsis thaliana

Prashant S Hosmani, Purdue University

Abstract

The development of the endodermis in the root plays a critical role in the radial transport of water and mineral nutrients into the root stele. Endodermal development begins with the formation of the Casparian strip, a chemically modified region of the cell wall which forms a belt-like structure at the anticlinal wall of the cells in the endodermis. The Casparian strip acts as a barrier to diffusion in the apoplast and provides the endodermal cell polarity that is essential for radial transport. The Casparian strip is primarily composed of lignin. In the region of the root just distal of the root tip the Casparian strip forms the only barrier to diffusion in the apoplast. However, as the endodermis develops in regions of the root distal to the site of primary Casparian strip deposition suberin lamellae are deposited in the apoplast which provides an extra barrier to diffusion. In spite of the critical role of the endodermis in water and solute transport very little is known about the biosynthetic mechanism of Casparian strip formation. Recently, the CASP family of proteins has been shown to be involved in the formation of the Casparian strip by playing an essential role in the formation of the Casparian strip membrane domain. Here, we determine that the Arabidopsis thaliana dirigent-like ESB1 protein localizes to the Casparian strip and expression of the ESB1 gene occurs in that region of the root in which the Casparian strip is developed but that region that lacks suberin lamellae. Importantly, loss of function of ESB1 leads to a malformed Casparian strip. Further, ectopic deposition of suberin in esb1 early in the development of the endodermis is likely to be responsible for the altered leaf ionome of esb1 and also its reduced transpiration. We also observe that in the casp1casp3 double mutant ESB1 is no longer localized to the Casparian strip. The development of the endodermis in the root plays a critical role in the radial transport of water and mineral nutrients into the root stele. Endodermal development begins with the formation of the Casparian strip, a chemically modified region of the cell wall which forms a belt-like structure at the anticlinal wall of the cells in the endodermis. The Casparian strip acts as a barrier to diffusion in the apoplast and provides the endodermal cell polarity that is essential for radial transport. The Casparian strip is primarily composed of lignin. In the region of the root just distal of the root tip the Casparian strip forms the only barrier to diffusion in the apoplast. However, as the endodermis develops in regions of the root distal to the site of primary Casparian strip deposition suberin lamellae are deposited in the apoplast which provides an extra barrier to diffusion. In spite of the critical role of the endodermis in water and solute transport very little is known about the biosynthetic mechanism of Casparian strip formation. Recently, the CASP family of proteins has been shown to be involved in the formation of the Casparian strip by playing an essential role in the formation of the Casparian strip membrane domain. Here, we determine that the Arabidopsis thaliana dirigent-like ESB1 protein localizes to the Casparian strip and expression of the ESB1 gene occurs in that region of the root in which the Casparian strip is developed but that region that lacks suberin lamellae. Importantly, loss of function of ESB1 leads to a malformed Casparian strip. Further, ectopic deposition of suberin in esb1 early in the development of the endodermis is likely to be responsible for the altered leaf ionome of esb1 and also its reduced transpiration. We also observe that in the casp1casp3 double mutant ESB1 is no longer localized to the Casparian strip.

Degree

Ph.D.

Advisors

Salt, Purdue University.

Subject Area

Plant biology|Genetics|Cellular biology

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