Organization and structural evolution of four multigene families in Arabidopsis thaliana: AtLCAD, AtLGT, AtMYST and AtHD-GL2

The Arabidopsis Genome Initiative has released up to now more than 80% of t he genome sequence of Arabidopsis thaliana. About 70% of the identified gen es have at least one paralogue. In order to understand the biological funct ion of individual genes, it is essential to study the structure, expression and organization of the entire multigene family. A systematic analysis of multigene families, made possible by the amount of genomic sequence data av ailable, provides important clues for the understanding of genome evolution and plasticity. In this paper, four multigene families of A. thaliana are characterized, namely LCAD, HD-GL2, LGT and MYST. Members of HD-GL2 and LCA D have already been reported in plants. The LGT genes specify proteins cont aining motifs of glycosyl transferase. No plant genes similar to the LGT ge nes have been reported to date. The novel MYST family, most likely plant-sp ecific, encodes proteins with no identified function. Sequencing and in sil ico analysis led to the characterization of 29 novel genes belonging to the se four gene families. The organization, structure and evolution of all the members of the four families are discussed, as well as their chromosome lo cation. Expression data of some of the paralogues of each family are also p resented.