Evolution of fruit size in tomato( where endemic wild populations of these...)

Date:6/27/2008

, where endemic wild populations of these species still grow. Tanksley and his colleagues have been employing the data emerging from the International Tomato Genome Sequencing Project as well as the tools of structural genomics to clone and characterize the major gene and QTL responsible for extreme fruit size during tomato domesticationfas.

The first QTL, fw2.2, was the first ever cloned in plants and may have been the site of one of the earliest mutations in tomato that led to its selection by humans and subsequent domestication. The size of tomato fruit can vary up to 30% as a result of variation at this locus alone. Cloning and sequencing of this locus reveals that the wild type protein codes for a repressor of cell division. When the control sequence is mutated, the repressor protein is not expressed or only very little, leading to higher cell division during fruit development and, consequently, larger fruits.

However, fw2.2 and associated genes related to cell-cycle control and cell division are not solely responsible for extreme fruit size. Two other loci-- locule-number and fasciated (fas)-- influence fruit size indirectly by affecting the number of carpels, the female parts of the flower that will become seed chambers in the fruit. Most wild tomatoes have only 2-4 locules (ovary chambers) while domesticated varieties can have 8 or more, and it appears that increase in locule number can increase fruit size by 50%. The data indicate that, of the two loci, fas has the larger effect. Tanksley and his colleagues used positional cloning to isolate the fas locus.

Sequencing suggested that the fas gene encodes a protein (YABBY-like transcription factor) that controls transcription of DNA into RNA as the first step of gene expression. It also revealed that there were no changes in the protein coding region of the gene but rather the mutation consisted of an insertion in the first intron, which is a non-coding sequence embed
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Contact: Dr. Luz Barrero lbarrero@corpoica.org.co 571-422-7329 American Society of Plant Biologists Source:Eurekalert

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