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Research Project: Genetic Mechanisms and Improvement of Insect Resistance in Wheat, Barley, and Sorghum

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Title: Genome-wide identification and classification of the Lipoxygenase gene family and their roles in sorghum-aphid interaction

item SHRESTHA, KUMAR - Oklahoma State University
item Pant, Shankar
item Huang, Yinghua

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2021
Publication Date: 1/2/2021
Citation: Shrestha, K., Pant, S.R., Huang, Y. 2021. Genome-wide identification and classification of the Lipoxygenase gene family and their roles in sorghum-aphid interaction. Plant Molecular Biology.

Interpretive Summary: Sorghum is an important crop grown worldwide and ranks fifth among the major cereal crops in terms of both production and area planted. But it is currently threatened by sugarcane aphid (SCA). Now SCA has already spread to more than twenty states in the U.S. and it has become a major pest of sorghum. It is believed that host plant resistance is the most economical and effective method to manage this pest. Thus, the current research at USDA-ARS Laboratory in Stillwater, Oklahoma has focused on studies of genetic mechanisms underlying host plant resistance in sorghum using the cutting-edge genomic approach. Lipoxygenase (LOX) pathway is crucial for plant defense responses to infection by pathogens and insects. Thus, researchers in this ARS laboratory have conducted a genome-wide analysis of the sorghum LOXs genome, which led to identification of all members of the LOX gene family, showing at least nine individual genes in this gene family. Of which each gene carries certain unique features though all family members share a high similarity at the DNA sequence level based on phylogenetic analysis. Furthermore, expression of those genes was investigated, which provided the evidences that some of the LOX genes are closely associated with plant responses to aphid attack, implying that those genes and their expression products play important roles in plant resistance to SCA. In summary, the new information generated from this study will facilitate future studies to characterize the roles of each individual LOXs gene in a stress-related function. This research will be of great interest to plant scientists and crop breeders in the future for genetic manipulation and breeding for better resistant varieties.

Technical Abstract: Lipoxygenases (LOXs) are monomeric, nonheme iron-containing dioxygenases that initiate the fatty acid oxidation pathway creating oxylipins and plant hormone jasmonate both have a key role in plant development and defense. To date, a comprehensive and systematic analysis of sorghum LOXs is still deficient. Thus, we have performed a genome-wide analysis of the sorghum LOXs genome and identified nine LOXs genes. Detailed examination of protein sequences and phylogenetic analysis categorized the sorghum LOXs into two classes, 9-LOXs (SbLOX1, SbLOX3, SbLOX4, SbLOXm, and SbLOXo), 13-LOXs (SbLOX9, SbLOX5, and SbLOX2), and the unclassified SbLOX8. This classification was further supported by sequence similarity/identity matrix and subcellular localization analysis. The lipoxygenase domains, motifs, and vital amino acids were highly conserved in all LOX genes of sorghum. Furthermore, in order to explore roles of sorghum LOXs during sugarcane aphid feeding and exogenous MeJA application, expression analysis was conducted for all the eight LOXs in resistant (Tx2783) and susceptible (Tx7000) sorghum lines, respectively. As detailed in this report, the data generated from both genome-wide identification and expression analysis of lipoxygenase genes suggest the putative functions of two 13-LOXs (SbLOX9 and SbLOX5) and three 9-LOXs (SbLOX1, SbLOX3, and SbLOXo) in biosynthesis of jasmonic acid, green leaf volatiles and death acids, and all of them are involved in defense-related functions in plants. Furthermore, this report represents the first genome-scale analysis of the LOX gene family in sorghum, which will facilitate future studies to characterize the roles of each individual LOXs genes in aphid resistance and defense responses to other biotic stresses.