Characterization of a novel DUF1618 gene family in rice

Domain of unknown function (DUF) proteins represent a number of gene families that encode functionally uncharacterized proteins in eukaryotes. For example, DUF1618 family members in plants possess a 56-199-amino acid conserved domain and this family has not been described previously. Here, we report the characterization of 121 DUF1618 genes identified in the rice genome. Based on phylogenetic analysis, the rice DUF1618 family was divided into two major groups, each group consisting of two clades. Most DUF1618 genes with close phylogenetic relationships are located in gene clusters on the chromosomes, indicating that gene duplications increased the number of DUF1618 genes. A search for DUF1618 genes in genomic and/or expressed sequence tag databases for 35 other plant species showed that DUF1618 genes are only present in several monocot plants, suggesting that DUF1618 is a new gene family that originated after the dicot-monocot divergence. Based on public microarray databases, most rice DUF1618 genes are expressed at relatively low levels. Further experimental analysis showed that the transcriptional levels of some DUF1618 genes varied in different cultivars, and some responded to stress and hormone conditions, suggesting their important roles for development and fitness in rice (Oryza sativa L.).