Characterization and Functional Divergence of a Novel DUF668 Gene Family in Rice Based on Comprehensive Expression Patterns

Abstract

The domain of unknown function (DUF) superfamily encodes proteins of unknown functions in plants. Among them, <i>DUF668</i> family members in plants possess a 29 amino-acid conserved domain, and this family has not been described previously. Here, we report this plant-specific novel <i>DUF668</i> gene family containing 12 <i>OsDUF668</i> genes in rice (<i>Oryza sativa</i>) and 91 <i>DUF668</i>s for the other seven plant species. In our study, <i>DUF668</i> genes were present in both dicot and monocot plants, indicating that <i>DUF668</i> is a conserved gene family that originated by predating the dicot-monocot divergence. Based on the gene structure and motif composition, the <i>DUF668</i> family consists of two distinct clades, I and II in the phylogenetic tree. Remarkably, <i>OsDUF668</i> genes clustered on the chromosomes merely show close phylogenetic relationships, suggesting that gene duplications or collinearity seldom happened. <i>Cis</i>-elements prediction display that over 80% of <i>DUF668s</i> contain phytohormone and light responsiveness factors. Further comprehensive experimental analyses of the <i>OsDUF668</i> family are implemented in 22 different tissues, five hormone treatments, seven environmental factor stresses, and two pathogen-defense related stresses. The <i>OsDUF668</i> genes express ubiquitously in analyzed rice tissues, and seven genes show tissue-specific high expression profiles. All <i>OsDUF668s</i> respond to drought, and some of Avr9/Cf-9 rapidly elicited genes resist to salt, wound, and rice blast with rapidly altered expression patterns. These findings imply that <i>OsDUF668</i> is essential for drought-enduring and plant defense. Together, our results bring the important role of the <i>DUF668</i> gene family in rice development and fitness to the fore.