AtGRP3 Is Implicated in Root Size and Aluminum Response Pathways in Arabidopsis.

AtGRP3 is a glycine-rich protein (GRP) from Arabidopsis thaliana shown to interact with the receptor-like kinase AtWAK1 in yeast, in vitro and in planta. In this work, phenotypic analyses using transgenic plants were performed in order to better characterize this GRP. Plants of two independent knockout alleles of AtGRP3 develop longer roots suggesting its involvement in root size determination. Confocal microscopy analysis showed an abnormal cell division and elongation in grp3-1 knockout mutants. Moreover, we also show that grp3-1 exhibits an enhanced Aluminum (Al) tolerance, a feature also described in AtWAK1 overexpressing plants. Together, these results implicate AtGRP3 function root size determination during development and in Al stress.

The tissue expression pattern of the AtGRP5 regulatory region is controlled by a combination of positive and negative elements.

The AtGRP5 gene from Arabidopsis thaliana encodes a glycine-rich protein which has a major activity in protoderm-derived cells and is expressed in cells that undergo the first anatomical modifications leading to somatic embryo development. It has been previously demonstrated that its minimum promoter is 316 bp long including the 5'UTR and presents three putative TATA-boxes sequences and several regions that are homologous to previous characterized cis-acting elements. In order to better characterize the AtGRP5 expression and to identify the promoter regions involved in its preferential epidermal expression, in situ hybridization and 5' promoter deletions were employed. In situ hybridization and GUS expression assays indicate that, besides being present during somatic embryogenesis, AtGRP5 is also expressed during the zygotic embryo development. The sequential 5' deletions indicate that multiple negative and positive regulatory elements are present in the AtGRP5 promoter and operate in order to confer its distinct expression pattern. A 44-bp region was shown to be essential for the epidermal expression of this gene in leaves, stems, flowers and fruits, and is also responsible for high activity of the AtGRP5 promoter in zygotic embryos. An element responsible for the phloem expression was also identified in a 35-bp region.

AtGRP5, a vacuole-located glycine-rich protein involved in cell elongation.

Although several glycine-rich protein (GRP) genes were isolated and characterized, very little is known about their function. The primary structure of AtGRP5 from Arabidopsis thaliana has a signal peptide followed by a region with high glycine content. In this work, green fluorescent protein fusions were obtained in order to characterize the sub-cellular localization of the AtGRP5 protein. The results indicated that this protein is the first described vacuolar GRP. Sense, antisense and RNAi transgenic A. thaliana plants were generated and analyzed phenotypically. Plants overexpressing AtGRP5 showed longer roots and an enhanced elongation of the inflorescence axis, while antisense and RNAi plants demonstrated the opposite phenotype. The analysis of a knockout T-DNA line corroborates the phenotypes obtained with the antisense and RNAi plants. Altogether, these results suggest that this vacuolar GRP could be involved in organ growth by promoting cell elongation processes.

AtGRP2, a cold-induced nucleo-cytoplasmic RNA-binding protein, has a role in flower and seed development.

The glycine-rich protein AtGRP2 is one of the four members of the cold-shock domain (CSD) protein family in Arabidopsis. It is characterized by the presence of a nucleic acid-binding CSD domain, two glycine-rich domains and two CCHC zinc-fingers present in nucleic acid-binding proteins. In an attempt to further understand the role of CSD/GRP proteins in plants, we have proceeded to the functional characterization of the AtGRP2 gene. Here, we demonstrate that AtGRP2 is a nucleo-cytoplasmic protein involved in Arabidopsis development with a possible function in cold-response. Expression analysis revealed that the AtGRP2 gene is active in meristematic tissues, being modulated during flower development. Down-regulation of AtGRP2 gene, using gene-silencing techniques resulted in early flowering, altered stamen number and affected seed development. A possible role of AtGRP2 as an RNA chaperone is discussed.

Survey of glycine-rich proteins (GRPs) in the Eucalyptus expressed sequence tag database (ForEST)

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

AtchitIV gene expression is stimulated under abiotic stresses and is spatially and temporally regulated during embryo development

The expression of AtchitIV gene was analysed in Arabidopsis plants submitted to abiotic stresses. Transcript accumulation was detected in leaves in response to UV light exposure, exogenous salicylic acid administration and wounding. Transgenic Arabidopsis plants carrying AtchitIV promoter::gus fusion also showed differential expression of the reporter gene in response to these treatments. The AtchitIV expression was also analysed during Arabidopsis embryo development. GUS assay demonstrated AtchitIV promoter activation in zygotic embryos from torpedo stage up to full maturation. Promoter deletion analysis indicated that all the 5' cis-acting elements responsible for the specific tissue expression are located in a region of 1083 bp, adjacent to the start of transcription. A negative regulatory region located between portions -1083 and -600 was also observed.