Floral genes expressed in tomato hypocotyl explants in liquid culture

This paper confirms, at molecular level, previous data showing that small e xplants of many plants do form a floral meristem and express specific flora l genes after only few days in culture. After 15-20 days of culture, small tomato hypocotyl explants develop differentiated structures often resemblin g primitive ancestral reproductive organs. Other specific reproductive func tions such as chromosomal segregation (somatic meiosis) were also present a nd demonstrated by means of a cytological and histological analysis. By rev erse transcriptase-PCR and in situ hybridization it was found that these st ructures are indeed able to express flower-specific genes. The TM8 gene, a tomato gene that is expressed very early during floral development, is dete ctable on the proliferating hypocotyl explants during the first week of cul ture. The MON9612 gene, which in vivo is expressed only by tomato pistils a nd ovules, is detectable on the ovulelike structures developed after 20 day s of culture. The construction of transgenic tomato plants expressing the G US gene under the control of the MON9612 promoter allowed us to follow the induction and the expression of this gene during explant proliferation and development of the flowerlike structures. These data confirm the hypothesis that a floral reprogramming can be induced in plant explants as a conseque nce of wounding and growth factors action. It appears to be an effort to su rvive stress by means of an unscheduled reproductive program.