Traffic lines: new tools for genetic analysis in Arabidopsis thaliana.

Genetic analysis requires the ability to identify the genotypes of individuals in a segregating population. This task is straightforward if each genotype has a distinctive phenotype, but is difficult if these genotypes are phenotypically similar or identical. We show that Arabidopsis seeds homozygous or heterozygous for a mutation of interest can be identified in a segregating family by placing the mutation in trans to a chromosome carrying a pair of seed-expressed green and red fluorescent transgenes (a "traffic line") that flank the mutation. Nonfluorescent seeds in the self-pollinated progeny of such a heterozygous plant are usually homozygous for the mutation, whereas seeds with intermediate green and red fluorescence are typically heterozygous for the mutation. This makes it possible to identify seedlings homozygous for mutations that lack an obvious seedling phenotype, and also facilitates the analysis of lethal or sterile mutations, which must be propagated in heterozygous condition. Traffic lines can also be used to identify progeny that have undergone recombination within a defined region of the genome, facilitating genetic mapping and the production of near-isogenic lines. We produced 488 transgenic lines containing single genome-mapped insertions of NAP:dsRED and NAP:eGFP in Columbia (330 lines) and Landsberg erecta (158 lines) and generated sets of traffic lines that span most regions of the Arabidopsis genome. We demonstrated the utility of these lines for identifying seeds of a specific genotype and for generating near-isogenic lines using mutations of WUSCHEL and SHOOTMERISTEMLESS. This new resource significantly decreases the effort and cost of genotyping segregating families and increases the efficiency of experiments that rely on the ability to detect recombination in a defined chromosomal segment.