The occurrence of quasi-repetitive glycine-rich peptides has been reported in different organisms. Glycine-rich regions are proposed to be involved in protein-protein interactions in some mammalian protein families. In plants, a set of glycine-rich proteins (GRPs) was characterized several years ago, and since then a wealth of new GRPs have been identified. GRPs may have very diverse sub-cellular localization and functions. The only common feature among all different GRPs is the presence of glycine-rich repeat domains. The expression of genes encoding GRPs is developmentally regulated, and also induced, in several plant genera, by physical, chemical and biological factors. In addition to the highly modulated expression, several GRPs also show tissue-specific localization. GRPs specifically expressed in xylem, phloem, epidermis, anther tapetum and roots have been described. In this paper, the structural and functional features of these proteins in Eucalyptus are summarized. Since this is the first description of GRPs in this species, particular emphasis has been given to the expression pattern of these genes by analyzing their abundance and prevalence in the different cDNA-libraries of the Eucalyptus Genome Sequencing Project Consortium (ForEST). The comparison of GRPs from Eucalyptus and other species is also discussed.

Desde o isolamento da primeira proteína rica em glicina (GRP) em plantas, um grande número de novas GRPs vem sendo identificado. Seu padrão de expressão altamente específico, embora variado, em conjunto com as diferentes localizações sub-celulares de alguns dos tipos de GRPs, claramente indica que estas proteínas encontram-se envolvidas em diversos processos fisiológicos independentes. Embora ainda sem uma clara definição do papel de GRPs na célula vegetal, estudos realizados com estas proteínas têm resultado em novos e interessantes esclarecimentos da biologia celular e molecular de plantas. Promotores com regulação complexa, assim como distintos mecanismos de regulação da expressão gênica tem sido demonstrados. Novas vias de endereçamento de proteínas tais como a exportação de GRPs para diferentes tipos celulares, tem sido observados. Estes dados mostram que as GRPs podem constituir marcadores e/ou modelos interessantes para a compreensão de distintos aspectos da biologia vegetal. Neste trabalho, características estruturais e funcionais deste tipo de proteínas em cana-de-açúcar (Saccharum officinarum L.) foram analisadas. Uma vez que esta é a primeira descrição deste tipo de proteínas em cana-de-açúcar, especial atenção foi dada para o padrão de expressão destes genes, analisando-se a abundância e prevalência de cada um dos genes nas diferentes bibliotecas de cDNA do projeto Sequenciamento de ESTs de cana-de-açúcar (SUCEST). A comparação das GRPs de cana-de-açúcar com as GRPs descritas em outras espécies também será discutida.

Since the isolation of the first glycine-rich proteins (GRPs) in plants a wealth of new GRPs have been identified. The highly specific but diverse expression pattern of grp genes, taken together with the distinct sub-cellular localization of some GRP groups, clearly indicate that these proteins are involved in several independent physiological processes. Notwithstanding the absence of a clear definition of the role of GRPs in plant cells, studies conducted with these proteins have provided new and interesting insights into the molecular biology and cell biology of plants. Complexly regulated promoters and distinct mechanisms for the regulation of gene expression have been demonstrated and new protein targeting pathways, as well as the exportation of GRPs from different cell types have been discovered. These data show that GRPs can be useful as markers and/or models to understand distinct aspects of plant biology. In this paper, the structural and functional features of these proteins in sugarcane (Saccharum officinarum L.) are summarized. Since this is the first description of GRPs in sugarcane, special emphasis has been given to the expression pattern of these GRP genes by studying their abundance and prevalence in the different cDNA-libraries of the Sugarcane Expressed Sequence Tag (SUCEST) project . The comparison of sugarcane GRPs with GRPs from other species is also discussed.