Abstract
Soybean (Glycine max [L.] Merr) is one of the main grain legumes worldwide. Soybean farmers lose billions of dollars’ worth of yield annually due to root and stem rot disease caused by the oomycete Phytophthora sojae. Many strategies have been developed to combat the disease, however, these methods have proven ineffective in the long term. A more cost effective and durable approach is to select a trait naturally found in soybean that can increase resistance. One such trait is the increased production of phytoalexin glyceollins in soybean. Glyceollins are isoflavonoids, synthesized via the legume-specific branch of general phenylpropanoid pathway. The first key enzyme exclusively involved in glyceollin synthesis is chalcone reductase (CHR) which coacts with chalcone synthase for the production of isoliquiritigenin, the precursor for glyceollin biosynthesis. Here we report the identification of 14 putative CHR genes in soybean where 11 of them are predicted to be functional. Our results show that GmCHRs display tissue-specific gene expression, and that only root-specific GmCHRs are induced upon P. sojae infection. Among 4 root-specific GmCHRs, GmCHR2A is located near a QTL that is linked to P. sojae resistance suggesting GmCHR2A as a novel locus for partial resistance that can be utilized for resistance breeding.
Highlights
Soybean (Glycine max [L.] Merr) is one of the most important grain legumes in the world
Since several QTL markers and QTLs linked to P. sojae resistance contained GmCHR gene family members, we evaluated the parental cultivars of QTL Phytoph 10-3 for root-specific GmCHR gene expression
The legume-specific enzyme chalcone reductase (CHR) together with chalcone synthase (CHS), converts 1 molecule of p-coumaroyl-CoA and 3 molecules of malonylCoA to isoliquiritigenin, the building block of two core isoflavone aglycones, glycitein and daidzein, where daidzein serves as a precursor for the production of phytoalexin glyceollins in soybean
Summary
Soybean (Glycine max [L.] Merr) is one of the most important grain legumes in the world. Partial resistance, referred to as field resistance, is more durable and a broadspectrum non-race-specific trait conferred by several minor genes which involves various defense components Cultivars with this type of resistance contain fewer damaged roots than completely susceptible cultivars, show delayed disease progression, and are effective against all races of P. sojae (Schmitthenner, 1985). Some key traits such as increased levels of soybean root suberin and increased production of phytoalexin glyceollins have been correlated with strong partial resistance in soybean (Thomas et al, 2007; Lygin et al, 2013). When isoflavonoid production was compromised by down regulating the biosynthetic genes, chalcone reductase (CHR) and isoflavone synthase (IFS), it reduced the plants’ ability to fight off the pathogen attack (Subramanian et al, 2005; Graham et al, 2007; Lozovaya et al, 2007)
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