Friday, July 6, 2012

How tomatoes lost their flavor

Breed­ers have un­know­ingly bred the fla­vor out of toma­toes by fa­vor­ing those with a nice un­iform col­or, sci­en­tists are re­port­ing. It’s hoped the find­ing could help grow­ers re­cap­ture the old, sweet fla­vor of toma­toes—which, as they sit on su­per­mar­ket shelves to­day, of­ten seem not to taste much dif­fer­ent from the pack­ag­ing they sit in. The find­ing, re­ported in the June 29 is­sue of the jour­nal Sci­ence, could have im­plica­t­ions for the U.S. to­ma­to in­dus­try, which har­vests over 15 mil­lion tons of the fruit yearly for pro­cess­ing and fresh-market sales. “This in­forma­t­ion… pro­vides a strat­e­gy to re­cap­ture qual­ity char­ac­ter­is­tics that had been un­know­ingly bred out of mod­ern cul­ti­vat­ed toma­toes,” said Ann Pow­ell, a bio­chem­ist at the Uni­vers­ity of Cal­i­for­nia Da­vis and one of the lead au­thors of the stu­dy. For about 70 years, breed­ers have se­lected to­ma­to va­ri­eties with un­iformly light green fruit be­fore rip­en­ing. These toma­toes then turn red evenly as they rip­en, and they look nice in a su­per­mar­ket dis­play. Pow­ell and col­leagues say the gene at the heart of un­iform rip­en­ing codes for the pro­duc­tion of a mol­e­cule called GLK2, which is a tran­scrip­tion fac­tor, mean­ing it go­verns ge­net­ic ac­ti­vity.
GLK2 boosts the fruit’s ca­pa­city for pho­to­syn­the­sis, the pro­cess of con­vert­ing sun­light to sug­ars, Pow­ell and col­leagues found. The mol­e­cule al­so aids the pro­duc­tion of ly­copene, a health pro­mot­ing com­pound. But the un­iform-rip­en­ing muta­t­ion dis­ables GLK2, the re­search­ers found. This leads to in­fe­ri­or de­vel­op­ment of pho­to­syn­the­sis-enabling cel­lu­lar struc­ture called choloro­plasts, and in turn, low­er pro­duc­tion of key in­gre­di­ents that give toma­toes their sweet­ness. Re­search­ers at the uni­vers­ity be­gan stu­dying the genes in­flu­enc­ing to­ma­to de­vel­op­ment and rip­en­ing af­ter screen­ing to­ma­to plants for cer­tain tran­scrip­tion fac­tors that might play a role in both col­or and qual­ity. They were par­tic­u­larly in­ter­est­ed in toma­toes they saw that were un­usu­ally dark green be­fore rip­en­ing. Part­ner­ing with re­search­ers at Cor­nell Uni­vers­ity in New York and in Spain, who were map­ping re­gions of the to­ma­to ge­nome, the sci­en­tists disco­vered two tran­scrip­tion fac­tors, GLK1 and GLK2, that con­trol the de­vel­op­ment of chloro­plasts. The re­search­ers scoured a col­lec­tion of mu­tant and wild spe­cies of toma­toes es­tab­lished at UC Da­vis by the late Pro­fes­sor Charles Rick be­gin­ning in the 1950s. They disco­vered that dark green toma­toes that nat­u­rally pro­duce GLK2 pro­duced ripe fruit with more sug­ars or sol­u­ble solids, im­por­tant for pro­cess­ing toma­toes, as well as more ly­copene.

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