The Cell Wall PAC (Proline-Rich, Arabinogalactan Proteins, Conserved Cysteines) Domain-Proteins Are Conserved in the Green Lineage.

Huan Nguyen-Kim,Elisabeth Jamet,Peter Lackner,Gabriele Gadermaier,Josef Laimer,Hélène San Clemente,Christophe Dunand

doi:10.3390/ijms21072488

Abstract

Plant cell wall proteins play major roles during plant development and in response to environmental cues. A bioinformatic search for functional domains has allowed identifying the PAC domain (Proline-rich, Arabinogalactan proteins, conserved Cysteines) in several proteins (PDPs) identified in cell wall proteomes. This domain is assumed to interact with pectic polysaccharides and O-glycans and to contribute to non-covalent molecular scaffolds facilitating the remodeling of polysaccharidic networks during rapid cell expansion. In this work, the characteristics of the PAC domain are described in detail, including six conserved Cys residues, their spacing, and the predicted secondary structures. Modeling has been performed based on the crystal structure of a Plantago lanceolata PAC domain. The presence of β-sheets is assumed to ensure the correct folding of the PAC domain as a β-barrel with loop regions. We show that PDPs are present in early divergent organisms from the green lineage and in all land plants. PAC domains are associated with other types of domains: Histidine-rich, extensin, Proline-rich, or yet uncharacterized. The earliest divergent organisms having PDPs are Bryophytes. Like the complexity of the cell walls, the number and complexity of PDPs steadily increase during the evolution of the green lineage. The association of PAC domains with other domains suggests a neo-functionalization and different types of interactions with cell wall polymers

Highlights

Plant cell walls are composite structures mainly made of polysaccharides and proteins
As a first step and in order to obtain a better definition of a PAC domain, orthologous sequences have been identified in the A. thaliana genome using that of the AtAGP31 PAC domain
Not been possible to identify with certainty a PAC domain ancestor in the presumed precursor organisms of the green lineage even if the C. orbicularis PAC domain appeared as a possible candidate

Summary

Introduction

Plant cell walls are composite structures mainly made of polysaccharides and proteins. Among the newly described CWPs families, the importance of the PAC (Proline-rich Arabinogalactan protein and Conserved Cysteines) domain containing-protein (PDP) family could be stressed because of their presence in many cell wall proteomes The following ones can be mentioned: Daucus carota DcAGP1 [12]; Arabidopsis thaliana AtAGP30 [13], and AtAGP31 (At1g28290) [14]; Capsicum annuum CaPRP1 [15]; Gossypium hirsutum GhAGP31 [16]; and Petunia hybrida PhPRP1 [17] It appeared that the PAC domain could be found alone, located at the N-terminus of the mature protein or associated with different types of domains, such as a Histidine-rich region, an O-glycosylated Proline/Hydroxyproline-rich domain, or an extensin domain [18,19]

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Conclusion