The SAC domain-containing protein gene family in Arabidopsis.

The SAC domain was first identified in the yeast (Saccharomyces cerevisiae) Sac1p phosphoinositide phosphatase protein and subsequently found in a number of proteins from yeast and animals. The SAC domain is approximately 400 amino acids in length and is characterized by seven conserved motifs. The SAC domains of several proteins have been recently demonstrated to possess phosphoinositide phosphatase activities. Sac1p has been shown to regulate the levels of various phosphoinositides in the phosphoinositide pool and affect diverse cellular functions such as actin cytoskeleton organization, Golgi function, and maintenance of vacuole morphology. The Arabidopsis genome contains a total of nine genes encoding SAC domain-containing proteins (AtSACs). The SAC domains of the AtSACs possess the conserved amino acid motifs that are believed to be important for the phosphoinositide phosphatase activities of yeast and animal SAC domain proteins. AtSACs can be divided into three subgroups based on their sequence similarities, hydropathy profiles, and phylogenetic relationship. Gene expression analysis demonstrated that the AtSAC genes exhibited differential expression patterns in different organs and, in particular, the AtSAC6 gene was predominantly expressed in flowers. Moreover, the expression of the AtSAC6 gene was highly induced by salinity. These results provide a foundation for future studies on the elucidation of the cellular functions of SAC domain-containing proteins in Arabidopsis.