Genome-wide identification and characterization of Xylanase Inhibitor Protein (XIP) genes in cereals

Xylanase inhibitor proteins (XIPs) have been reported to be involved in plant defense mechanisms, more predominantly against fungal pathogens. XIPs have mostly been well characterized in model plant species, and very little is known about their distribution, organization and evolution in cereals. In the present study, we have identified XIPs in four cereal plant species, including three major crops sorghum, maize, rice and a model species Brachypodium. The genome-wide analysis identified 10, 20, 13 and 31 XIP genes respectively for Brachypodium, sorghum, maize and rice. The number of identified genes is in well accordance with the genome size except for maize. Interestingly, most of the XIP genes were observed to be intron-less, and clustered together on the chromosomes. The XIP genes organization is much similar to the lower eukaryotes and fungi suggesting the possibility of horizontal gene transfer from the pathogen. The phylogenetic analysis of XIP revealed two major groups, and minor subgroups mostly representing gene clusters. Gene expression evaluation using publically available data suggested LOC_Os11g47500 and LOC_Os11g47510are candidate genes for resistance against Magnaporthe grisea pathogen in rice. The information provided here would be helpful for the identification of candidate resistance genes in other cereals.