Understanding Floral Development and Sex Expression in Dioecious Coccinia grandis

Coccinia grandis (Cucurbitaceae) is a dioecious plant with heteromorphic X and Y chromosomes. Male and female plants have 22+XY and 22+XX chromosomes respectively. Y chromosome is conspicuously large and plays a decisive role in determining maleness. Our recent investigations on sexual phenotypes of C. grandis including a rare gynomonoecious (GyM) form and AgNO₃ mediated sex modification have added a new dimension to the understanding of sex expression in dioecious flowering plants. Phenotypic analysis revealed the presence of staminodes in pistillate flowers and histological study showed the absence of carpel initials in male flowers. Y chromosome was absent in gynomonoecious (GyM) plants but the development of stamens occurred in hermaphrodite flowers and the pollens were sterile. Additionally, in wild type female flowers enhanced stamen growth was observed with AgNO₃ application but the pollens were not fertile. Results from qRT-PCR indicated that CgPI expression could be associated with the developmental variation in floral phenotypes. Regulation of sex expression in dioecious C. grandis could be controlled by three important factors such as Gynoecium Suppression (Su^F), Stamen Promoting Factor (SPF) and Male Fertility (m^F), which are assumed to be located on Y chromosome and play a decisive role in determining maleness. On contrary, the stamen development in hermaphrodite flowers of GyM plant with XX sex chromosomes specifies that Y-linked SPF regulatory pathway is by some means detoured. Taken together, our results suggest that C. grandis could be utilized as a potential model system to study sex expression in dioecious flowering plant.