The origin and evolution of plant cystatins and their target cysteine proteinases indicate a complex functional relationship.

Manuel Martinez,Isabel Diaz

doi:10.1186/1471-2148-8-198

Abstract

BackgroundCystatins and their putative targets, the families of cysteine proteinases C1A and C13 play key roles in plants. Comparative genomic analyses are powerful tools to obtain valuable insights into the conservation and evolution of the proteinases and their proteinaceous inhibitors, and could aid to elucidate issues concerning the function of these proteins.ResultsWe have performed an evolutionary comparative analysis of cysteine proteinases C1A and C13 and their putative inhibitors in representative species of different taxonomic groups that appeared during the evolution of the Viridiplantae. The results indicate that whereas C1A cysteine proteinases are present in all taxonomic groups, cystatins and C13 cysteine proteinases are absent in some basal groups. Moreover, gene duplication events have been associated to the increasing structural and functional complexities acquired in land plants.ConclusionComparative genomic analyses have provided us valuable insights into the conservation and evolution of the cystatin inhibitory family and their putative targets, the cysteine proteinases from families C1A and C13. Functionality of both families of proteins in plants must be the result of a coevolutionary process that might have occurred during the evolution of basal and land plants leading to a complex functional relationship among them.

Highlights

Cystatins and their putative targets, the families of cysteine proteinases C1A and C13 play key roles in plants
The results indicate that whereas papain-like cysteine proteinases are present in all taxonomic groups, cystatins and legumain-like proteins are absent in some basal groups
The presence of any species of each clade with a transcript assemblies (TA) belonging to the cystatin family, or to the papain-like or legumain-like cysteine proteinase families is represented

Summary

Introduction

Cystatins and their putative targets, the families of cysteine proteinases C1A and C13 play key roles in plants. One of them corresponds to a family of peptidase inhibitors called cystatins, which constitute a superfamily of evolutionary related proteins able to inhibit cysteine proteinases from the papain subfamily C1A. Those from plants are called phytocystatins (PhyCys) and form an independent subfamily that cluster on a distinct branch from other cystatin families on the phylogenetic tree [3]. Several PhyCys with a molecular mass of ≈ 23 kDa have a carboxy-terminal extension, which has been involved in the inhibition of a second family of cysteine peptidases, the legumain peptidases C13 [6]. They have been (page number not for citation purposes)

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Conclusion