fw2.2: A Quantitative Trait Locus Key to the Evolution of Tomato Fruit Size

Rcjohnsen rcjohnsen at aol.com
Sat Jul 8 16:15:43 EST 2000

fw2.2: A Quantitative Trait Locus Key to the Evolution of Tomato Fruit Size 

Anne Frary, 1* T. Clint Nesbitt, 1* Amy Frary, 1 Silvana Grandillo, 1 Esther
van der Knaap, 1 Bin Cong, 1 Jiping Liu, 1 Jaroslaw Meller, 2 Ron Elber, 2
Kevin B. Alpert, 1 Steven D. Tanksley 1§ 
Domestication of many plants has correlated with dramatic increases in fruit
size. In tomato, one quantitative trait locus (QTL), fw2.2, was responsible for
a large step in this process. When transformed into large-fruited cultivars, a
cosmid derived from the fw2.2 region of a small-fruited wild species reduced
fruit size by the predicted amount and had the gene action expected for fw2.2.
The cause of the QTL effect is a single gene, ORFX, that is expressed early in
floral development, controls carpel cell number, and has a sequence suggesting
structural similarity to the human oncogene c-H-ras p21. Alterations in fruit
size, imparted by fw2.2 alleles, are most likely due to changes in regulation
rather than in the sequence and structure of the encoded protein.  
1 Department of Plant Breeding and Department of Plant Biology, 252 Emerson
Hall, Cornell University, Ithaca, NY 14853, USA. 
2 Department of Computer Science, Cornell University, Ithaca, NY 14853, USA. 
*   These authors contributed equally to this work. 

   Present address: Department of Biological Sciences, Clapp Laboratory, Mount
Holyoke College, South Hadley, MA 01075, USA.  

   Present address: Research Institute for Vegetable and Ornamental Plant
Breeding, IMOF-CNR, Via Universita 133, 80055 Portici, Italy. 

§   To whom correspondence should be addressed. 

In natural populations, most phenotypic variation is continuous and is effected
by alleles at multiple loci. Although this quantitative variation fuels
evolutionary change and has been exploited in the domestication and genetic
improvement of plants and animals, the identification and isolation of the
genes underlying this variation have been difficult.  

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