The Gene Family in Rice: Molecular Characterization, Transport Functions and Expression Analysis.

Amino acid transporters (AATs) are integral membrane proteins and play important roles in plant growth and development as well as environmental responses. In contrast to the amino acid permease (AAP) subfamily, functional studies of the lysine and histidine transporter (LHT) subfamily have not been made in rice. In the current study, six genes were found in the rice genome. To further investigate the functions of these genes, analyses were performed regarding gene and protein structures, chromosomal locations, evolutionary relationships, cis-acting elements of promoters, gene expression, and yeast complementation. We found that the six genes are distributed on 4 out of the 12 chromosomes and that the six genes were grouped into two clusters based on the phylogenetic analysis. Protein structure analyses showed that each OsLHT protein has 11 helical transmembrane domains. Yeast complementation assays showed that these Os genes have conserved transport substrates within each cluster. The four members from cluster 1 showed broad amino acid selectivity, while OsLHT5 and OsLHT6 may transport other substrates besides amino acids. Additionally, quantitative real-time PCR analysis of the six genes revealed that they have different expression patterns at different developmental stages and in different tissues. It also revealed that some genes were responsive to PEG, NaCl and cold treatments, indicating their critical roles in abiotic stress response. Our results will be useful for further characterizing the crucial biological functions of rice genes.