The effects of the C1 regulatory gene: a biochemical and genetic study of the anthocyanin pathway in Zea mays

摘要

The biosynthesis of anthocyanins by plants involves a complex cascade of reactions. In maize over 20 loci are known to affect the expression of the anthocyanin pathway. The easy access to mutants, their non-lethality and diversity make this pathway an ideal model for examining questions about pathway regulation, including tissue specificity and timing of expression: gene structure and function; and the nature of quantitative traits;This study examines the C1 locus regulation of anthocyanin pathway expression in developing maize endosperm (aleurone) tissue. Four different alleles of the C1 locus are used for comparison. These included: C-I(A69), a dominant color-inhibiting allele; C-(lineC), a dominant color-expressing allele; c-ruq66, a recessive colorless allele (Uq absent) containing a transposon insertion; and c, a stable recessive colorless allele. Each of these alleles were converted to a common genetic background and their expression in endosperm examined at five stages during kernel maturation;This study measures the accumulation of specific anthocyanin pathway products as a means of identifying C1 locus action. These compounds are UDPglucose:flavonoid 3-O-glucosyltransferase (UFGT), caffeic acid-glucoside, [rho]-coumaric acid, quercetin-3-glucoside, quercetin-7-glucoside, quercetin-3,7-diglucoside, quercetin-3-sophoroside, quercetin-3-sophoroside-7-glucoside, quercetin-3-(caffeoylsophoroside)-7-glucoside, peonidin-3-(caffeylrutinoside)-5-glucoside, peonidin-3-([rho]-coumarylrutinoside)-5-glucoside, and malvidin-3-(caffeylrutinoside)-5-glucoside. This is the first report in maize of the last six compounds listed;Developmental profiles of compound accumulation were constructed for a glucosyltransferase and each of the observed substituted cinnamic acids, flavonol glycosides, and anthocyanins. As expected, UFGT activity only increased above background levels in pigmented, C-(lineC) tissue. However, quercetin utilization was highest in young unpigmented (18 and 27 days after pollination) tissue regardless of genotype. This corresponds to the observed early accumulation of several quercetin glycosides and suggests the presence of other glycosyltransferases;In general, the colored, C-(lineC), and colorless, C-I(A69) and c genotypes accumulated increasing levels of flavonol glycosides and substituted cinnamic acids with increasing endosperm maturity. The colorless, c-ruq66, genotype expressed the reverse trend with the highest accumulation levels in young endosperm;In contrast, only the colored, C-(lineC), endosperm tissue accumulated significant anthocyanins. The accumulation maximums were 180 to 210 times greater than the values for the colorless genotypes.