The Arabidopsis seedpod opens through a spring-loaded mechanism known as pod shatter, which is essential for dispersal of the seeds. Here, we identify INDEHISCENT (IND), an atypical bHLH protein, that is necessary for fruit opening and is involved in patterning each of the three fruit cell types required for seed dispersal. Previous studies suggested that FRUITFULL (FUL), a member of the MADS-domain transcription factor family, is required for fruit growth since ful mutant fruit fail to undergo the dramatic enlargement that normally occurs after fertilization. Here we show, however, that FUL is not directly required for fruit elongation and instead is required to prevent ectopic activity of IND. Our molecular and genetic studies suggest a model for the regulatory interactions among the genes that control fruit development and the mechanism that results in the expression of IND in a narrow stripe of cells.

Genetic studies demonstrate that two Arabidopsis genes, CAULIFLOWER and APETALA1, encode partially redundant activities involved in the formation of floral meristems, the first step in the development of flowers. Isolation of the CAULIFLOWER gene from Arabidopsis reveals that it is closely related in sequence to APETALA1. Like APETALA1, CAULIFLOWER is expressed in young flower primordia and encodes a MADS-domain, indicating that it may function as a transcription factor. Analysis of the cultivated garden variety of cauliflower (Brassica oleracea var. botrytis) reveals that its CAULIFLOWER gene homolog is not functional, suggesting a molecular basis for one of the oldest recognized flower abnormalities.

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Mutations in the AGAMOUS (AG) gene of Arabidopsis tbaliana result in the conversion of reproductive organs, stamens and carpels, into perianth organs, sepals and petals. We have isolated and characterized the putative AC gene from Nicotiana fabacum, NAG1, whose deduced protein product shares 73% identical amino acid residues with the Arabidopsis AG gene product. RNA tissue in situ hybridizations show that NACl RNA accumulates early in tobacco flower development in the region of the floral meristem that will later give rise to stamens and carpels. Ectopic expression of NACl in transgenic tobacco plants results in a conversion of sepals and petals into carpels and stamens, respectively, indicating that NACl is sufficient to convert perianth into reproductive floral organs.

We have assembled an integrated genetichestriction fragment length polymorphism (RFLP) linkage map of the nuclear genome of the flowering plant Arabidopsis thaliana. The map is based on two independent sets of RFLP data, RFLP data for 123 new markers, and pairwise segregation data of 125 classical genetic markers. Mathematical integration of the independent data sets was performed using the JOINMAP computer package. Sixty-two markers common to two or more data sets were exploited to facilitate integration of the individual maps. The current map, which encompasses a total genetic distance of 520 cM, contains 125 classical genetic markers and 306 RFLP markers.Comparison of the integrated consensus map with the individual maps demonstrates that the overall linear order of the integrated map is in good agreement with the component maps. It must be emphasized, however, that the integrated map represents the 'best fit' which is clearly subject to the statistical limitations of the available data. We present several examples where local differences in map order are observed between the integrated and component maps. It is likely, given the problems associated with statistical