The Sorghum Gene for Leaf Color Changes upon Wounding (P) Encodes a Flavanone 4-Reductase in the 3-Deoxyanthocyanidin Biosynthesis Pathway

Abstract

Upon wounding or pathogen invasion, leaves of sorghum [Sorghum bicolor (L.) Moench] plants with the P gene turn purple, whereas leaves with the recessive allele turn brown or tan. This purple phenotype is determined by the production of two 3-deoxyanthocyanidins, apigeninidin and luteolinidin, which are not produced by the tan-phenotype plants. Using map-based cloning in progeny from a cross between purple Nakei-MS3B (PP) and tan Greenleaf (pp) cultivars, we isolated this gene, which was located in a 27-kb genomic region around the 58.1 Mb position on chromosome 6. Four candidate genes identified in this region were similar to the maize leucoanthocyanidin reductase gene. None of them was expressed before wounding, and only the Sb06g029550 gene was induced in both cultivars after wounding. The Sb06g029550 protein was detected in Nakei-MS3B, but only slightly in Greenleaf, in which it may be unstable because of a Cys252Tyr substitution. A recombinant Sb06g029550 protein had a specific flavanone 4-reductase activity, and converted flavanones (naringenin or eriodictyol) to flavan-4-ols (apiforol or luteoforol) in vitro. Our data indicate that the Sb06g029550 gene is involved in the 3-deoxyanthocyanidin synthesis pathway.

Expression of Flavone Synthase II and Flavonoid 3′-Hydroxylase Is Associated with Color Variation in Tan-Colored Injured Leaves of Sorghum

“…F3′H hydroxylates the 3′ position of the B-ring of naringenin to produce eriodictyol; both are called flavanones (Boddu et al, 2004; Shih et al, 2006). FNR converts flavanones (naringenin or eriodictyol) to flavan-4-ols (apiforol or luteoforol, respectively), and this is followed by the synthesis of 3-deoxyanthocyanidins (apigeninidin or luteolinidin, respectively; Kawahigashi et al, 2016). FNSII converts flavanones (naringenin or eriodictyol) to flavones (apigenin or luteolin, respectively; Du et al, 2010).…”

“…The color depends on the sorghum cultivar. For example, the leaves of Nakei-MS3B and JN43 turn purple; those of bmr-6 turn reddish orange; those of BTx623 turn orange (Mizuno et al, 2014); and those of M36001, JP501, JP43800, JP588, JP43764, and Greenleaf turn tan (brown; Kawahigashi et al, 2016). Moreover, it is possible to distinguish light or dark brown colorations in plants with tan colors (Doggett, 1988).…”

“…The protein encoded by the P gene is flavanone 4-reductase (FNR), which is responsible for the synthesis of 3-deoxyanthocyanidins (Kawahigashi et al, 2016). The variation of purple-red-orange is explained by the balance of two 3-deoxyanthocyanidins (luteolinidin and apigeninidin; Mizuno et al, 2014).…”

“…The FNR gene of JP501 and JP43800 has an insertion in the coding region; those of Greenleaf, JP588, and JP43764 have a Cys252Tyr amino acid substitution and encode unstable protein (Kawahigashi et al, 2016). Sorghums with a tan injury response have lower levels of flavan-4-ols (precursors of apigeninidin and luteolinidin—apiforol and luteoforol, respectively) than do sorghums with a purple or red injury response (Dykes et al, 2005); they are thus unable to synthesize 3-deoxyanthocyanidins.…”

The wheat Lr34 multipathogen resistance gene confers resistance to anthracnose and rust in sorghum

“…Flavonoid phytoalexin and anthocyanidin biosynthetic pathway (Kawahigashi et al ., ; Liu et al ., ). Genes highlighted in red and products circled were quantified in this study.…”