Interaction Between Induced and Natural Variation at oil yellow1 Delays Reproductive Maturity in Maize

Abstract

We previously demonstrated that maize (Zea mays) locus very oil yellow1 (vey1) encodes a putative cis-regulatory expression polymorphism at the magnesium chelatase subunit I gene (aka oil yellow1) that strongly modifies the chlorophyll content of the semi-dominant Oy1-N1989 mutants. The vey1 allele of Mo17 inbred line reduces chlorophyll content in the mutants leading to reduced photosynthetic output. Oy1-N1989 mutants in B73 reached reproductive maturity four days later than wild-type siblings. Enhancement of Oy1-N1989 by the Mo17 allele at the vey1 QTL delayed maturity further, resulting in detection of a flowering time QTL in two bi-parental mapping populations crossed to Oy1-N1989. The near isogenic lines of B73 harboring the vey1 allele from Mo17 delayed flowering of Oy1-N1989 mutants by twelve days. Just as previously observed for chlorophyll content, vey1 had no effect on reproductive maturity in the absence of the Oy1-N1989 allele. Loss of chlorophyll biosynthesis in Oy1-N1989 mutants and enhancement by vey1 reduced CO2 assimilation. We attempted to separate the effects of photosynthesis on the induction of flowering from a possible impact of chlorophyll metabolites and retrograde signaling by manually reducing leaf area. Removal of leaves, independent of the Oy1-N1989 mutant, delayed flowering but surprisingly reduced chlorophyll contents of emerging leaves. Thus, defoliation did not completely separate the identity of the signal(s) that regulates flowering time from changes in chlorophyll content in the foliage. These findings illustrate the necessity to explore the linkage between metabolism and the mechanisms that connect it to flowering time regulation.

Variation in maize chlorophyll biosynthesis alters plant architecture

“…The single locus testing of oy1-vey1 interactions for these traits were tested directly using NIL x tester crosses. We found stalk widths of Oy1-N1989 mutants were narrower than wildtype siblings and this was enhanced by the vey1 Mo17 allele, just as we previously found for chlorophyll content, net CO2 assimilation, and time to reproductive maturity (Khangura et al 2019a(Khangura et al , 2019b. To our surprise, we found that plant height in the Oy1-N1989 mutants can be either greater or less than their congenic wildtype siblings.…”

“…The plant height and stalk width were measured in both wildtype (WT) and mutant (MT) siblings segregating in each family in the F1 populations of Oy1-N1989/+:B73 with the IBM , Syn10, and NIL populations. As described previously (Khangura et al 2019a(Khangura et al , 2019b, genetic backgrounds containing the vey1 B73 allele progressively suppresses the mutant phenotype and were tagged at V5-V7 stage when they were distinguishable from the wildtype siblings so that traits could be recorded at maturity when the genotypes are harder to distinguish. Trait measurements were performed on two to four WT and MT siblings that were picked at random.…”

“…The genotypic and gene expression datasets used in this study are described previously in detail (Khangura et al 2019a(Khangura et al , 2019b. Briefly, the public marker data for IBM consists of 2,156 unique markers.…”

“…The highly heritable vey1 QTL is a major modifier of chlorophyll contents in heterozygous Oy1-N1989/+ mutants but had no effect on chlorophyll accumulation in wildtype plants from either B73 x Mo17 biparental mapping populations or a maize association panel (Khangura et al 2019a). The vey1 alleles are detectable as a cis-acting eQTL and generate allele-specific expression at oy1 (Li et al 2013(Li et al , 2018Waters et al 2017;Khangura et al 2019aKhangura et al , 2019b. These expression level differences at oy1 are visible at the mRNA level in both mutants and wildtypes, but the impact on chlorophyll content was only visible in the presence of the Oy1-N1989 allele (Khangura et al 2019a).…”

“…Using the Oy1-N1989 mutant allele, and the two vey1 modifier alleles from B73 and Mo17, we previously developed populations of maize to investigate the effects of this cryptic variant on chlorophyll content (Khangura et al 2019a), net CO2 assimilation, and reproductive maturity (Khangura et al 2019b). These three phenotypes showed high linear correlations with each other and were consistent with expression of the wildtype oy1 allele such that greater expression of the wildtype OY1 transcript resulted in suppression of the Oy1-N1989/+ mutant phenotype (Khangura et al 2019a(Khangura et al , 2019b. Our results, thus far, are consistent with an integrative measure of carbon assimilation linking energy status and vegetative to reproductive transition in maize (Minow et al 2018).…”