Germins and germin-like proteins: Plant do-all proteins. But what do they do exactly?

Abstract

Germins and germin-like proteins (GLPs) constitute a large and highly diverse family of ubiquitous plant proteins. The name germin was given because the first described member of the family, wheat germin, was discovered in germinating wheat grains. However, it is now known that proteins from this family exist in all organs and developmental stages and that several are also involved in the response to various stress conditions. It is thus increasingly obvious that germins and GLPs participate in many processes that are important for plant development and defence. However, their exact participation in these processes generally remains obscure so the main challenge now is to determine the precise activities and functions of all germins and GLPs. Molecular and biochemical studies are contributing to a better understanding of this protein family and much data has accumulated in the last 2 years. All species possess a wide range of GLPs and each GLP gene is subjected to a tight regulation. All germins and GLPs are glycoproteins somehow associated with the extracellular matrix. More specifically, three classes of functions are starting to be recognized for these proteins: some possess an enzymatic activity (oxalate oxidase or superoxide dismutase), others seem to be structural proteins while some others act as receptors. To explain the diversity and ubiquitousness of germins and GLPs, we propose that most, if not all, of them carry out a combination of different functions.