Transgenic rice expressing isoflavone synthase gene from soybean shows resistance against blast fungus (Magnaporthe oryzae)

Authors: POKHREL, SURESH - University Of Arkansas At Pine Bluff; PONNIAH, SATHISH - University Of Arkansas At Pine Bluff; Jia, Yulin; YU, OLIVER - Conagen, Inc; MANOHARAN, MUTHUSAMY - University Of Arkansas At Pine Bluff

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2021
Publication Date: 2/22/2021
Citation: Pokhrel, S., Ponniah, S.K., Jia, Y., Yu, O., Manoharan, M. 2021. Transgenic rice expressing isoflavone synthase gene from soybean shows resistance against blast fungus (Magnaporthe oryzae). Plant Disease. https://doi.org/10.1094/PDIS-08-20-1777-RE.
DOI: https://doi.org/10.1094/PDIS-08-20-1777-RE

Interpretive Summary: Rice blast disease caused by the fungus Magnaporthe oryzae (M. oryzae) is one of the most lethal diseases of rice worldwide. The product of isoflavones especially genistein is a precursor for the production of phytoalexins - antimicrobial compounds that induce broad-spectrum disease resistance. Rice does not contain isoflavone and it is unknown if products of isoflavone including genistein from soybean and maize can be used to provide effective resistance to rice blast fungus M. oryzae. In the present study, we expressed three isoflavone biosynthetic genes, soybean chalcone synthase (CHS) and soybean isoflavone synthase (IFS) genes and the maize transcriptional factor C1/R (CRC) in rice and evaluated transgenic lines for rice blast reactions at University of Arkansas at Pine Bluff. We found transgenic lines with enhanced levels of genistein also with enhanced blast resistance for each transgene. The greatest level of blast resistance was observed in transgenic lines expressing all three transgenes. The enhanced blast resistance correlated with the amount of genistein, suggests that genistein is involved in reducing the damage by M. oryzae. These findings provide a novel method of controlling rice blast disease via a genetic engineering approach.

Technical Abstract: The isoflavones are a group of plant secondary metabolites primarily synthesized in legumes and are known for their role in human health and plant disease resistance. The isoflavones, especially genistein, acts as precursors for the production of phytoalexins, antimicrobial compounds, which may induce broad-spectrum disease resistance. Such an important plant secondary metabolite like isoflavones is lacking in rice. Here we expressed three isoflavone biosynthetic genes in rice for disease resistance. The chalcone synthase (CHS) and isoflavone synthase (IFS) genes from soybean and the transcriptional factor C1/R from maize (CRC) were heterologously expressed in rice and resulting transgenic lines were evaluated with a strain of Magnaporthe oryzae. Progenies of two independent events from each IFS, CHS, and CRC homozygous transgenic lines showed more than 50% resistance to M. oryzae. Similarly, progenies of double or triple transgenes stacked lines showed more than 60% blast resistance. The genistein analysis revealed triple transgenes (CHS x IFS x CRC) containing line showed the highest genistein production (569.12 ng/g) followed by two transgenes (CHS x IFS) containing line (370.2 ng/g). The blast resistance observed is more likely due to the genistein production in transgenic lines produced by introduced isoflavones biosynthetic genes in rice.