August 23, 2006
Source: Proceedings of the
National Academies of Sciences of the United States of America
http://www.pnas.org/cgi/content/abstract/0604635103v1?etoc
Overdominant quantitative trait
loci for yield and fitness in tomato
Yaniv
Semel, Jonathan Nissenbaum,
Naama Menda, Michael Zinder, Uri Krieger, Noa Issman,
Tzili Pleban, Zachary Lippman, Amit Gur, and Dani
Zamir
Institute of
Plant Sciences and Genetics, Faculty of Agriculture, Hebrew
University of Jerusalem
Edited by Susan R. Wessler,
University of Georgia, Athens, GA, and approved July
7, 2006 Heterosis,
or hybrid vigor, is a major genetic force that contributes
to world food production. The genetic basis of
heterosis is not clear, and the importance of loci
with overdominant (ODO) effects is debated. One
problem has been the use of whole-genome segregating
populations, where interactions often mask the effects of
individual loci. To assess the contribution of ODO to
heterosis in the absence of epistasis, we carried out
quantitative genetic and phenotypic analyses on a
population of tomato (Solanum lycopersicum)
introgression lines (ILs), which carry single marker-defined
chromosome segments from the distantly related wild
species Solanum pennellii. The ILs revealed
841 quantitative trait loci (QTL) for 35 diverse
traits measured in the field on homozygous and
heterozygous plants. ILs showing greater reproductive fitness
were characterized by the prevalence of ODO QTL, which
were virtually absent for the nonreproductive traits.
ODO can result from true ODO due to allelic
interactions of a single gene or from pseudoODO that
involves linked loci with dominant alleles in
repulsion. The fact that we detected dominant and recessive
QTL for all phenotypic categories but ODO only for the
reproductive traits indicates that pseudoODO due to
random linkage is unlikely to explain heterosis in
the ILs. Thus, we favor the true ODO model involving
a single functional Mendelian locus. We propose that
the alliance of ODO QTL with higher reproductive fitness
was selected for in evolution and was domesticated by man
to improve yields of crop plants.
Freely available online through
the PNAS open access option:
http://www.pnas.org/cgi/reprint/0604635103v1 |