Introduction

Mutants affecting sexual development in plants are relatively rare. Most of them concern cytoplasmic or nuclear male sterility, while a series of meiotic mutants in maize are well characterised (Kaul & Murthy, 1985). Other mutants, of the sex conversion type, have been described in maize and cucumber, two monoecious plants (Irish & Nelson, 1989; Malepszy & Niemerowicz-Szczytt, 1991).

Among flower pattern mutants, those affecting floral organs in whorls 2 and 3 exhibit various degrees of homeotic transformation of stamens into carpels e.g. apetala3 in Arabidopsis thaliana and deficiens in snapdragon (Jack, Brockman & Meyerowitz, 1992; Schwarz-Sommer et al., 1990). The corresponding genes have been cloned and represent transcription factors belonging to the MADS class.

We have recently described two asexual mutants in the dieocious Melandrium album, following irradiation of pollen with low doses of gammarays (Veuskens et al., 1992). Briefly, the mutants 5K63 and 8K40 have normal perianth organs (sepals and petals), while lacking both male and female reproductive organs: vestigial stamens and a ‘finger-like projection’ instead of carpels are present in whorls 3 and 4 respectively. Both mutants have a deletion covering respectively 12 and 21% of the Y-chromosome.

Here we report on the use of these asexual/Y deletion mutants in cDNA subtraction cloning and exploit them in refining the current understanding of sex determination in a plant X/Y system