Location: Wheat, Sorghum and Forage Research
Project Number: 3042-21220-034-002-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Mar 1, 2022
End Date: Dec 31, 2025
The effectiveness of ‘silver bullet’ approaches such as pesticides and Bt (transgenic) crops to combat insect pests have diminished lately. Therefore, alternative approaches based on detailed understanding of host plant resistance and defense mechanisms could significantly accelerate the development of plants that are better able to resist insect attack. The goal of this proposal is to improve the understanding of the role of the monolignol pathway, which leads to the synthesis of lignin, in sorghum defense against sugarcane aphid (SCA). The sorghum Brown midrib6 (Bmr6) and Bmr12 genes encode for cinnamyl alcohol dehydrogenase (CAD) enzyme that catalyzes the conversion of hydroxycinnamoyl aldehydes to monolignols and caffeic acid O-methyltransferase (COMT) enzyme responsible for catalysis of penultimate step in lignin biosynthesis pathway, respectively. In SC- infested plants, comparable numbers of SCA were found on bmr6 and Bmr6-overexpressing (OE) plants. In contrast, loss of Bmr12 function and overexpression of Bmr12 (Bmr12 OE) resulted in increased resistance and susceptibility to SCA as compared with the wild-type plants, respectively. Our central hypothesis is that the monolignol pathway is involved in promoting plant defense against SCA and Bmr12 is a key component of this defense mechanism. To test this hypothesis, we will address the following objectives: objective 1 identify Bmr12-dependent regulatory mechanisms that are involved in providing sorghum defense against SCA; objective 2 characterize Bmr12’s involvement in sorghum defense against SCA; objective 3 determine Bmr12-dependent direct and indirect defenses that modulate sorghum defenses against SCA; and objective 4 develop and deliver multidisciplinary educational training programs in plant-insect interactions. ARS will directly participate in research objectives 1, 2 and 3.
Bmr12-dependent regulatory mechanisms that are involved in providing sorghum defense against sugarcane aphids (SCA) will be determined through RNA-seq and metabolomic profiling at early and late time points after SCA infestation. Target analyses of soluble and wall-bound hydroxcinnamoyl compounds will be performed using GC-MS to determine how SCA infestation affects these compounds derived from the monolignol pathway in addition to lignin. Microscopy and histochemical staining will be used to monitor lignin and hydroxycinnamoyl compound deposition within secondary cell walls following SCA infestation, which is both sensitive to alteration in monolignol biosynthesis and able to accommodate single leaf samples. These experiments will further the understandings of these mechanisms facilitating SCA resistance in bmr12 sorghum, which may lead to novel strategies of aphid resistance in sorghum and other grasses.