QTL analysis of popping fold and the consistency of QTLs under two environments in popcorn.

Popping fold (PF) is the most important quality trait in popcorn. In this study, a total of 259 F2:3 families, derived from the cross between a dent corn inbred Dan232 and a popcorn inbred N04, were evaluated for their popping folds in replicated experiments under two environments. Of 613 simple sequence repeat (SSR) primer pairs screened, 183 pairs were selected to construct a genetic linkage map with the genetic distance of 1,762.2 cM (centimorgan) and on average 9.63 cM every marker. Quantative trait loci (QTL) were identified, and their genetic effects were estimated using CIM (composite interval mapping) method. The interactions among QTLs detected were calculated using MIM (multiple interval mapping) method. In all, 22 QTLs were detected, and only 5 of them were common under two environments. Contribution to phenotypic variation of a single QTL varied from 3.07% to 12.84%, and total contributions of all QTLs under two environments were 66.46% and 51.90%, respectively. Three QTLs (qPF-6-1, qPF-8-1 and qPF-1-3) with more than 10% contributions were observed. The additive effects were larger than dominant effects for most QTLs. The amount of QTLs showing additive, partially dominant, dominant and over-dominant effects were 4, 5, 0, 2 in spring sowing and 2, 5, 2, 2 in summer sowing, respectively. There were only 2.60% pairs of QTLs or maker intervals expressing AA, DA or DD interactions.

[QTL analysis of starch content in maize kernels using the trisomic inheritance of the endosperm model].

Two hundred and fifty-nine F2:3 families, developed from the cross between a dent corn inbred line Dan232 and a popcorn inbred line N04, were evaluated for its starch content in the replicated experiments under two environments. One hundred and eighty three pairs of SSR markers were selected to construct a genetic linkage map, covering 1,762.2 cM (centiMorgan) and on the average distance of 9.63 cM between the markers. Quantative trait loci (QTL) were identified and its effects were analyzed, using the triploid endosperm genetic model and the interval mapping method. Ten QTL, detected on chromosome 1, 3, 4, 5 and 7 respectively, were mapped in spring and in summer. All detected QTL in spring were also identified in summer. The phenotypic variation of a single QTL varied from 4.74% to 11.26%, and the total contributions of all QTL under two environments were 36.84% and 72.65%, respectively. Two QTL of all identified QTL in spring showed over-dominant effects, but additive and partially dominant in summer respectively, the amounts of other QTL showing Additive, partially dominant and over-dominant effects were 2, 1, 5 respectively. The positive alleles of three QTL were contributed by the normal corn parent Dan232, and the other positive alleles were contributed by the popcorn parent N04.

Map-based cloning of zb7 encoding an IPP and DMAPP synthase in the MEP pathway of maize.

IspH is a key enzyme in the last step of the methyl-D-erythritol-4-phosphate (MEP) pathway. Loss of function of IspH can often result in complete yellow or albino phenotype in many plants. Here, we report the characterization of a recessive mutant of maize, zebra7 (zb7), showing transverse green/yellow striped leaves in young plants. The yellow bands of the mutant have decreased levels of chlorophylls and carotenoids with delayed chloroplast development. Low temperature suppressed mutant phenotype, while alternate light/dark cycle or high temperature enlarged the yellow section. Map-based cloning demonstrated that zb7 encodes the IspH protein with a mis-sense mutation in a conserved region. Transgenic silencing of Zb7 in maize resulted in complete albino plantlets that are aborted in a few weeks, confirming that Zb7 is important in the early stages of maize chloroplast development. Zb7 is constitutively expressed and its expression subject to a 16-h light/8-h dark cycle regulation. Our results suggest that the less effective or unstable IspH in zb7 mutant, together with its diurnal expression, are mechanistically accounted for the zebra phenotype. The increased IspH mRNA in the leaves of zb7 at the late development stage may explain the restoration of mutant phenotype in mature stages.