Phylogeny, structural evolution and functional diversification of the plant PHOSPHATE1 gene family: a focus on Glycine max

BACKGROUND: PHOSPHATE1 (PHO1) gene family members have diverse roles in plant growth and development, and they have been studied in Arabidopsis, rice, and Physcomitrella. However, it has yet to be described in other plants. Therefore, we surveyed the evolutionary patterns of genomes within the plant PHO1 gene family, focusing on soybean (Glycine max) due to its economic importance. RESULTS: Our data show that PHO1 genes could be classified into two major groups (Class I and Class II). Class I genes were only present and expanded in dicotyledonous plants and Selaginella moellendorffii; Class II genes were found in all land plants. Class I sequence losses in other lineages may be attributed to gene loss after duplication events in land plant evolution. Introns varied from 7 to 14, and ancestral state reconstruction analyses revealed that genes with 13 introns were ancestral, thus suggesting that the intron loss was a chief constituent of PHO1 gene evolution. In the soybean genome, only 12 PHO1-like genes (GmaPHO1) were detected at the mRNA level. These genes display tissue-specific or tissue-preferential expression patterns during soybean plant and fruit development. Class I genes were more broadly expressed than Class II. GmaPHO1 genes had altered expression in response to salt, osmotic, and inorganic phosphate stresses. CONCLUSIONS: Our study revealed that PHO1 genes originated from a eukaryotic ancestor and that two major classes formed in land plants. Class I genes are only present in dicots and lycophytes. GmaPHO1genes had diverse expression patterns in soybean, indicating their dramatic functional diversification.