Abstract
Powdery mildew (PM) is an important plant fungal disease that adversely affects a broad range of angiosperm species, including grass families such as wheat and barley. The MLO (powdery mildew locus O) protein acts as a negative regulator in PM-resistance. Loss-of-function mutation in MLO shows complete resistance to PM disease. In this study, for the first time we reported MLO gene family members in Brachypodium distachyon, model species for grass. 11 well-conserved BdMLO genes were identified on all five chromosomes with a scattered occurrence rather than clustered. The subcellular localization and topology analyses confirmed that all BdMLO proteins anchored to plasma membrane. The seven trans-membrane (TM) and calmodulin-binding domain (CaMBD) sites were well conserved. Amino acid composition showed that BdMLO proteins were leucine-rich (9.9-13.1 %) except BdMLO5 and BdMLO8, which were alanine-rich (10.0 %) and serine-rich (8.7 %), respectively. In silico functional dissection of cis-acting elements revealed that BdMLOs were associated with mainly hormonal, stress, light response and tissue-specific signaling pathways. Phylogenetic relations of BdMLOs within distinct plant species (Arabidopsis, barley, wheat, maize, rice, tomato, pea, pepper and peach) were evaluated. Also, digital expressions of BdMLOs in drought, cold and pathogen infection conditions revealed stress-responsive MLO genes. Phylogenetic and expression analyses provided preliminary evidence that BdMLO2 could be the best susceptibility gene which may play important role in PM resistance. It was concluded that identification and characterization of MLO gene members in Brachypodium will provide essential knowledge for studying full-scale functional analysis of these genes in grass species.