Location: Molecular Plant Pathology
Project Number: 8042-21220-231-00
Start Date: Jul 23, 2013
End Date: Jul 22, 2018
Sugar beet root defense genes incited by the root maggot, a destructive pest of sugar beet, will be characterized using molecular approaches to facilitate screening of sugar beet germplasm for resistance and to devise novel strategies for pest and disease control. Root genes identified as being important in plant defense will be expressed in susceptible plants and screened for enhanced levels of insect pest and phytopathogen resistance. Two resistance genes that preferentially respond to maggot feeding in a moderately resistant germplasm will be studied. One of these genes codes for a serine proteinase inhibitor (PI; BvSTI), and the other for a cell wall polygalacturonase inhibitor (PGIP, BvPGIP). BvSTI is a wound-inducible Kunitz trypsin PI with specificity for the root maggot digestive enzymes that mediate release of essential nutrients from ingested plant tissues. The second gene, BvPGIP, codes for a leucine-rich repeat glycoprotein PGIP associated with cell wall structure and plant defense responses. The role of the sugar beet BvSTI and BvPGIP genes in mediating resistance will be determined by transferring the recombinant genes into sugar beet hairy roots and model whole plants (Nicotiana and Arabidopsis). Genetically modified plants will be bioassayed for resistance to insect pests and phytopathogens. Insect bioassays will include fall armyworm, beet armyworm, or tobacco hornworm larvae and phytopathogens Aphanomyces cochlioides and Fusarium oxysporum that cause root rot in sugar beet. To more precisely target the expression of resistance genes to root cells and tissues most prone to pest and pathogen attack, root tissue-specific and temporal promoters will be identified, cloned, and functionally characterized by differential screening of sugar beet root EST libraries. Cloned promoters will be fused with a reporter gene (GUS) in a plant transformation vector and introduced into sugar beet hairy roots and model whole plants. Various biotic and abiotic stresses such as infestation with insect pests, infection with phytopathogens, mechanical wounding, and treatment with defense response elicitors such as methyl jasmonate and salicylic acid will be used to localize GUS gene expression driven by the selected sugar beet promoters. In complementary studies of insect responses, root maggot genes that are important in resistant and susceptible interactions with the sugar beet root will be identified. Root maggot genes will be profiled, sequenced, and functionally annotated to gain new knowledge of how insects adapt to host plants and surmount host resistance. Expression patterns of identified root maggot genes will be examined to confirm that the selected insect genes are specificity-expressed as a response to feeding on the sugar beet root.