Characterization of a deletion allele of a sorghum Myb gene, yellow seed1 showing loss of 3-deoxyflavonoids

In sorghum, 3-deoxyflavonoid pigments or phlobaphenes observed in the pericarp, of mature seed are derived from flavan-4-ols through the flavonoid biosynthetic pathway. We show here that phlobaphenes accumulation in pericarp, glumes and leaves is genetically linked with the functional yellow seed1 (y1) gene. Molecular and genetic analysis was performed on a loss of function allele of y1 present in the line BTx623. This sorghum line does not accumulate any detectable levels of flavan-4-ols or visible phlobaphenes in pericarp, glumes and leaves. Molecular structure of the y1 [BTx623] showed a deletion of 3218 bp which removes 5' non-coding, putative promoter, exon 1, intron 1, exon2, and part of the intron2 sequences. The null y1 allele designated as y1-ww (white pericarp, white glume) is not transcribed and this results in a loss of Y1-regulated expression of structural genes needed for the biosynthesis of flavan-4-ols. Further LC-MS analysis of seed extracts of a functional yl allele detected the presence of positively charged compounds known as 3-deoxyanthocyanidins. Compounds identified were apigeninidin, luteolinidin, and a methoxylated derivative of apigeninidin. The se compounds were not detected in BTx623 seed extracts. Previous studies have shown that 3-deoxyanthocyanidins are induced in sorghum leaves challenged with Colletotrichum sublineolum, a fungus that causes anthracnose in sorghum. Our results now provide an evidence for a common flavonoid pathway that may lead to the biosynthesis of flavan-4-ols and 3-deoxyanthocyanidins in sorghum. (c) 2005 Elsevier Ireland Ltd. All rights reserved.