Insights into Late Embryogenesis Abundant (LEA) Proteins in Plants: From Structure to the Functions

Late Embryogenesis Abundant (LEA) proteins, a group of hydrophilic proteins, have been linked to survival in plants and animals in periods of stress, putatively through safeguarding enzymatic function and prevention of aggregation in times of dehydration/heat. Yet despite decades of effort, the molecular-level mechanisms defining this protective function remain unknown. In this paper, we summarize and review research discoveries of the classification of the LEA protein groups based on their amino acid sequence similarity and on the presence of distinctive conserved motifs. Moreover, we focus on high correlation between their accumulation and water deficit, reinforcing their functional relevance under abiotic stresses. We also discuss the biochemical properties of LEA proteins arising from their hydrophilic nature and by amino acid composition. Although significant similarities have not been found between the members of the different groups, a unifying and outstanding feature of most of them is their high hydrophilicity and high content of glycine. Therefore, we have highlighted the biotechnological applications of LEA genes, and the effects of over-expressing LEA genes from all LEA groups from different species of origin into different plant hosts. Apart from agronomical purposes, LEA proteins could be useful for other biotechnological applications in relation to their capacity to prevent aggregation of proteins.

Osmotic Stress Resistance of Transgenic Tobacco Expressed Soybean Lysine-rich Protein Gene

PM2 gene （accession number： M80664） with high lysine content from soybean （Glycine max） was found in GenBank by changing three BLASTp parameters. Amino acid composition analysis of PM2 showed that Lys content was on the high level of 18.22%. Protein encoded by PM＇2 also belonged to the family of late embryogenesis abundant （LEA） proteins, which was considered that it had a strong relation with the abiotic stress resistance. In this experiment, PM2 gene was obtained from dry soybean seeds by RT-PCR, plant expression vector pEMTPM2 was constructed, and then transformed into tobacco by using agrobacterium-mediated method. Eight salt and drought tolerant lines were obtained from 31 differentiated lines. Real-time PCR showed that PM2 gene overexpressed in all four PCR positive lines with the osmotic stress resistance. These results confirmed that the overexpression of PM2 gene enhanced the osmotic stress resistance of transgenic tobacco.

Two New Group 3 LEA Genes of Wheat and Their Functional Analysis in Yeast

The group 3 late embryogenesis abundant （LEA） proteins are thought to protect cells from stresses associated with dehydration during periods of water deficit. To investigate the functions of different members of the group 3 LEA genes, we isolated and characterized two new group 3 LEA genes, namely TaLEA2 and TaLEA3, from wheat （Triticum aestivum L.） and introduced TaLEA2 and TaLEA3 into Saccharmyces cerevisiae to examine the effect of these genes on yeast cell tolerance to osmotic, salt, and cold stresses. The TaLEA2 gene encoded a protein of 211 amino acids and possessed five repeats of 11-mer amino acid motifs. The TaLEA3 gene encoded a polypeptide of 211 amino acids with nine repeated units. Overexpression of TaLEA2 and TaLEA3 improved stress tolerance in transgenic yeast cells when cultured in medium containing sorbitol, salt and-20℃ freezing treatments respectively. However, the yeast transformants with TaLEA2 seemed to be more tolerant to hyperosmotic and freezing stress than transformants with TaLEA3. This implies that a close relationship exists between function and the number of repeats of the 11- mer amino acid motif in the group 3 LEA protein.