Isolation and developmental expression of male reproductive organ-specific genes in a dioecious campion, Melandrium album (Silene latifolia).
The dioecious campion Melandrium album (Silene latifolia) has sex chromosomes, and male and female plants form different unisexual flowers. The very youngest buds have both sex organs but the development of either a gynoecium in the male bud or stamens in the female bud is arrested as the bud matures. To examine the molecular mechanism of male-specific differentiation, a cDNA library from male buds was differentially screened with cDNA from male and female buds. Four male reproductive organspecific cDNAs (corresponding to genes designated MROS1, MROS2, MROS3 and MROS4, respectively) were isolated. Northern blot analysis showed that the transcripts of MROS genes were expressed only in male reproductive organs. The transcripts of MROS3 and MROS4 accumulated in the early buds, while transcripts of MROS1 and MROS2 accumulated in the late buds and in the anthers of open flowers. The putative MROS2 protein has glycine-rich regions, while the putative MROS3 protein exhibits no similarity to known proteins. Genomic Southern blot analysis showed that male and female genomes included MROS2 and MROS3 genes. Non-radioactive in situ hybridization revealed the localization of the transcripts of MROS2 and MROS3 in male buds. MROS3 mRNA was distributed throughout the tapetum. After MROS2 mRNA had accumulated in the epidermis and the endothecium near the stomium, the accumulation of the mRNA increased significantly in the mature pollen. MROS2 seems to be a novel anther-specific gene that functions in dehiscence of anthers and the maturation of pollen.