Genome-wide analysis of the LEA (late embryogenesis abundant) protein gene family in Populus trichocarpa

Late embryogenesis abundant (LEA) proteins are a large and highly diverse group of polypeptides that are believed to function in desiccation and freezing tolerance in plants. This report presents a genome-wide analysis of LEA proteins and their encoding genes in Populus trichocarpa. Fifty-three LEA genes were identified from the Populus genome and divided into eight groups. The LEA4 and LEA5 groups were found in green algae and all land plants, whereas the other six groups existed only in land plants, indicating that the LEA family underwent rapid expansion during the early evolution of land plants. A majority of Populus LEA proteins contained repeated motifs that were often specific to a LEA group. Except for PtLEA2-1 and PtLEA2-3, all Populus LEA proteins were highly hydrophilic. Examination of the chromosomal locations of Populus LEA genes revealed that 30 % were arranged in tandem repeats, indicating that tandem duplications significantly contributed to the expansion of this gene family in Populus. Expression patterns of all Populus LEA genes under normal growth conditions and abiotic stress (salinity and drought) were investigated by reverse transcription polymerase chain reaction. Twelve of 53 Populus LEA genes were selectively expressed in a specific tissue and/or in response to a specific treatment. LEA genes also showed extensive divergence in expression patterns, even among those from the same group or gene cluster. The expression profiles revealed that the Populus LEA gene family was not involved systematically in the same regulatory pathway.