Mapping genes governing flower architecture and pollen development in a double mutant population of carrot

Abstract

A linkage map of carrot (Daucus carota L.) was developed in order to study reproductive traits. The F2 mapping population derived from an initial cross between a yellow leaf (yel) chlorophyll mutant and a compressed lamina (cola) mutant with unique flower defects of the sporophytic parts of male and female organs. The genetic map has a total length of 781 cM and included 285 loci. The length of the nine linkage groups (LGs) ranged between 65 and 145 cM. All LGs have been anchored to the reference map. The objective of this study was the generation of a well-saturated linkage map of D. carota. Mapping of the cola-locus associated with flower development and fertility was successfully demonstrated. Two MADS-box genes (DcMADS3, DcMADS5) with prominent roles in flowering and reproduction as well as three additional genes (DcAOX2a, DcAOX2b, DcCHS2) with further importance for male reproduction were assigned to different loci that did not co-segregate with the cola-locus.

Keywords: Daucus carota; MADS-box genes; alternative oxidase; chalcone synthase; linkage map; male gametogenesis.

Figure 1

Characterization of the phenotype classes. (A) Representative plants of the four phenotype classes I–IV in the F₂ segregating population DM19 obtained from a cross between mutants yel and cola. From left to right: wild-type plant with green and normal leaf structure (I); yel-mutant (II); cola-mutant (III); yel/cola double mutant (IV) (Bar = 10 cm). (B) Morphology of reproductive organs. Left: epigynous flower of wild-type. Right: hypogynous flower of cola-mutant (Bars = 1.0 mm). (C) Histo-morphological sections of flowers. Left: wild-type. Right: cola-mutant. Black arrowheads: petals, yellow arrowheads: ovule (Bars = 0.5 mm). (D) FDA pollen staining. Fertile pollen grains revealed a intensive greenish stain, whereas sterile and undeveloped pollen grains were stained weakly; Left: wild-type, Right: cola-mutant, arrowheads indicate undeveloped microspores.

Figure 2

Genetic map of carrot (Daucus carota L.) based on the F₂ population DM19. The anchor markers to the carrot reference map (Cavagnaro et al., 2011) are highlighted in green color and designated by the corresponding linkage group number in parenthesis. The newly mapped genes governing flower architecture and pollen development are marked in red. Distances are given on the left of the linkage groups.