Sex determination in papaya: Current status and perspectives

Papaya (Carica papaya L.) is an economically significant plant that produces fruit consumed worldwide due to its organoleptic characteristics. Since their commercial production, papaya fruits have faced several problems, such as pests, which have been partly resolved using transgenic varieties. Nevertheless, a principal challenge in this cultivation is the plant's sex determination. The sex issue in papaya is complex because papaya flowers can bear three sex forms: male, female, and hermaphrodite, which affects their fruit production, shape, and yield. Fruits from hermaphrodite plants are preferred more by consumers than female ones, and male plants rarely produce fruits without commercial value. Chromosomes are responsible for sex determination in papaya, denoted as XY for male, XX for female, and XYh for hermaphrodite. However, genes related to sex have been reported but are not conclusive. Factors such as the environment, hormones, and genetic and epigenetic background can also affect sex expression. Therefore, in this review, we will discuss recent research on the sex of papaya, from reported genes to date, their biology, and sexing approaches using molecular markers and their advantages.

Review: Isoprenoid and aromatic cytokinins in shoot branching

Shoot branching is an important event of plant development that defines growth and reproduction. The BRANCHED1 gene (BRC1/TB1/FC1) is crucial for this process. Within the phytohormones, cytokinins directly activate axillary buds to promote shoot branching. In addition, strigolactones and auxins inhibit bud outgrowth. This review addresses the involvement of aromatic and isoprenoid cytokinins in shoot branching. And how auxins and strigolactones contribute to regulating this process also. The results obtained by others and our working group with lemongrass (Cymbopogon citratus) show that cytokinins affect both shoot and root apical meristem development, consistent with other plant species. However, many questions remain about how cytokinins and strigolactones antagonistically regulate BRC1 gene expression. Additionally, many details of the interaction among cytokinins, auxins, and strigolactones need to be clarified. We will gain a more comprehensive scheme of bud outgrowth with these details.