TOMATO FLOWER ABNORMALITIES INDUCED BY LOW-TEMPERATURES ARE ASSOCIATED WITH CHANGES OF EXPRESSION OF MADS-BOX GENES

Flower and fruit development in tomato (Lycopersicon esculentum Mill.) were severely affected when plants were grown at low temperatures, di splaying homeotic and meristic transformations and alterations in the fusion pattern of the organs. Most of these homeotic transformations m odified the identity of stamens and carpels, giving rise to intermedia te organs. Complete homeotic transformations were rarely found and alw ays affected organs of the reproductive whorls. Meristic transformatio ns were also commonly observed in the reproductive whorls, which devel oped with an excessive number of organs. Scanning electron microscopy revealed that meristic transformations take place very early in the de velopment of the flower and are related to a significant increase in t he floral meristem size. However, homeotic transformations should occu r later during the development of the organ primordia. Steady-state re vels of transcripts corresponding to tomato MADS-box genes TM4, TM5, T M6, and TAG1 were greatly increased by low temperatures and could be r elated to these flower abnormalities. Moreover, in situ hybridization analyses showed that low temperatures also altered the stage-specific expression of TM4.