Oxysterol binding proteins (OSBPs) and their encoding genes in Arabidopsis and rice

Cell wall deposition, biosynthesis of steroid hormones, and maintenance of membrane composition and integrity, are some of the crucial functions of sterols in plants. Followed by their synthesis in the endoplasmic reticulum, the sterols accumulate in the plasma membrane. The concept of sterol trafficking in plant cell is not well understood. The oxysterol binding proteins are implicated in sterol transport in non-plant systems. In the study, the oxysterol binding proteins in Arabidopsis and rice are described and classified. The Arabidopsis genome encodes 12 oxysterol binding proteins-related proteins (ORPs) as compared to 6 oxysterol binding proteins (OSBPs/ORPs) in rice. The protein alignment studies reveal that amino acid sequences for oxysterol binding proteins are relatively well conserved in Arabidopsis and rice. The rice OSBPs are classified based on their phylogenetic relationship with Arabidopsis ORPs. The sequence LOGO built on LOC_Os03g16690 indicated presence of fingerprint region of amino acids "EQVSHHPP" for Arabidopsis and rice OSBPs/ORPs. The organization of pleckstrin homology domain is identified in several OSBPs/ORPs in Arabidopsis and rice. The Arabidopsis oligonucleotide array data is explored to understand the expression patterns of ORPs under 17 different experimental conditions. The analysis showed the expression of ORPs in Arabidopsis is necessarily under the control of biotic stress, chemical, elicitor, hormone, light intensity, abiotic stress, and temperature conditions. The linear mean signal values for Arabidopsis ORPs revealed their relative expression patterns in different developmental stages. The genes for ORP3C and ORP3B are highly expressed in all developmental stages that were analyzed. The present study thus indicates crucial functional role of the individual members of this gene family in different environmental stress conditions.