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

Abstract

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, exon1, intron1, 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 y1 allele detected the presence of positively charged compounds known as 3-deoxyanthocyanidins. Compounds identified were apigeninidin, luteolinidin, and a methoxylated derivative of apigeninidin. These 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.