Identification of novel Mlo family members in wheat and their genetic characterization.

Mlo is a plant-specific gene family, which is known to show stress responses in various plants. To reveal the genetic characteristics of the Mlo family in wheat, we isolated wheat Mlo members from a database and studied their expression in young shoots and roots under salt and osmotic stress conditions. In an in silico investigation, we identified seven Mlo members in wheat and named them TaMlo-1~TaMlo-7. None of the wheat Mlo showed significant induction or reduction of their expression under salt or osmotic stress, but organ-specific expression was observed in several TaMlo members. TaMlo-1, TaMlo-2, and TaMlo-5 were constitutively expressed in both shoots and roots, but TaMlo-3 and TaMlo-4 showed root-specific expression, and TaMlo-7 showed dominant expression in shoots. TaMlo-6 was weakly expressed in both shoots and roots. Phylogenetic analysis classified the plant Mlo members into six classes; four of them were comprised of angiosperm Mlo members, and the remaining two consisted of fern and moss Mlo members. The seven wheat Mlo members were classified into four angiosperm Mlo classes, similar to those of Arabidopsis and rice, indicating that the formation of each of the Mlo classes preceded the divergence of dicots and monocots. The differentiation of the expressional patterns among the seven TaMlo members was not related to their phylogenetic classification. This result suggested that the organ specific expression of individual Mlo members occurred relatively recently in their evolution.