Spatial Expression and Functional Analysis of Casparian Strip Regulatory Genes in Endodermis Reveals the Conserved Mechanism in Tomato.

Pengxue Li,Haiyang Qin,Abidur Rahman,Junqing Wu,Meina Yang,Shuang Wu,Jiang Chang,Fenglin Zhong

doi:10.3389/fpls.2018.00832

Pengxue Li, Haiyang Qin + Show 6 more

Open Access

https://doi.org/10.3389/fpls.2018.00832

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Abstract

Casparian strip (CS) is an impregnation of endodermal cell wall, forming an apoplastic diffusion barrier which forces the symplastic and selective transport of nutrients across endodermis. This extracellular structure can be found in the roots of all higher plants and is thought to provide the protection of vascular tissues. In Arabidopsis, a genetic toolbox regulating the formation of Casparian strips has emerged recently. However, Arabidopsis has the stereotypical root which is much simpler than most other plant species. To understand the Casparian strip formation in a more complex root system, we examined CS regulatory pathways in tomato. Our results reveal a spatiotemporally conserved expression pattern of most essential components of CS machinery in tomato. Further functional analyses verify the role of homologous CS genes in the Casparian strip formation in tomato, indicating the functional conservation of CS regulatory cascade in tomato.

Highlights

Despite varied cell layers in ground tissues, most vascular plants have only one endodermal layer surrounding the transporting vessel tissues in their roots (Lim et al, 2000; Enstone et al, 2003; Cui et al, 2007)
Formed together with vascular tissues during evolution (Heath, 1976; Enstone et al, 2003; Yoon et al, 2015), Casparian strips are present in ferns, gymnosperms and angiosperms, and some pinales (Warmbrodt and Evert, 1979; Pant and Basu, 1997; Wu et al, 2005)
The hydrophobic feature of Casparian strips makes it a protective structure for vascular tissues in plants which help to defend against various environmental stresses (Stasovski and Peterson, 1993; Karahara et al, 2004; Chen et al, 2011; Pfister et al, 2014; Yang et al, 2015; Yoon et al, 2015; Kamiya et al, 2015; Liberman et al, 2015; Liska et al, 2016; Le Roy et al, 2017; Li et al, 2017)

Summary

Introduction

Despite varied cell layers in ground tissues, most vascular plants have only one endodermal layer surrounding the transporting vessel tissues in their roots (Lim et al, 2000; Enstone et al, 2003; Cui et al, 2007). Endodermis functions as a barrier between inner stele tissues and outer ground tissues. When endodermal cells of the root begin to mature, a ring-like hydrophobic structure appears on the radial and transverse cell walls, named Casparian strip (CS). This unique structure forms a paracellular transport barrier to disrupt the free diffusion of water and nutrients, enforcing the selective transport between stele and outer cortex via symplastic transport or membrane associated transporters (Heath, 1976; Schreiber and Franke, 2011). The emergence of Casparian strip-like structures can be traced back to the root of ferns living about 400 million years ago (Moore et al, 2010; Geldner, 2013)

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