|Price, R Ruth|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2005
Publication Date: 4/1/2005
Citation: Cooper, L.D., Doss, R.P., Price, R.R., Nelson, K., Oliver, J.E. 2005. Application of Bruchin B to pea pods results in the up-regulation of CYP93C18, a putative isoflavone synthase gene, and an increase in the level of pisatin, an isoflavin phytoalexin. Journal of Experimental Botany. 56(414): 1229-1237. Interpretive Summary: Bruchins are chemical compounds associated with the eggs of certain insects, most notably pea weevils, that stimulate cell division when applied to pods of peas and some related legumes. This cell division results in the formation of wart-like growths that inhibit entry into the pod of the larvae of the insects that laid the eggs. Hence, the plant, by detecting and responding to the bruchin, is able to resist infestation by the insect, and it can be said that bruchins mediate a mechanical defense response. In this work we show that in addition to stimulation of cell division, application of bruchins to pea pods causes changes in expression of a gene that is involved in synthesis of a chemical defense compound; namely the isoflavone pisatin. Although this compound is normally thought to be involved in defending pea plants against fungal pests, it is possible that it is also active against insects.
Technical Abstract: Bruchins, mono- and bis-(3-hydroxypropanoate) esters of long chain alpha, omega-diols, are a recently discovered class of insect elicitors that stimulate cell division and neoplasm formation when applied to pods of peas and certain other legumes. An mRNA whose level was increased by application of bruchin B to pods of pea plants was identified using differential display, the corresponding cDNA fragment was cloned and sequenced and a full length cDNA sequence was obtained. This cDNA and the gene from which it was derived were assigned the name CYP93C18 based upon sequence similarities to the CYP93C subfamily of cytochrome P450 monooxygenases, a subfamily containing isoflavone synthase genes from legumes. RNA gel blots and quantitative real-time RT-PCR demonstrated that expression of CYP93C18 increased within 8 hours of bruchin treatment to a maximum of 100- to 200-fold the level in untreated pods and then declined. The up-regulation of CYP93C18 was followed by an increase in the level of the isoflavone phytoalexin, pisatin. Pisatin was detectable in the bruchin treated pods after 16 hours and reached a maximum between 32 and 64 hours. This, the first report of induction of phytoalexin biosynthesis by an insect elicitor, suggests that bruchins not only stimulate neoplasm formation, but also activate other plant defense responses.