Papaya (Carica papaya) is a trioecious plant species that has male, female and hermaphrodite flowers on different plants. The primitive sex chromosomes genetically determine the sex of the papaya. Although draft sequences of the papaya genome are already available, the genes for sex determination have not been identified, likely due to the complicated structure of its sex-chromosome sequences. To identify the candidate genes for sex determination, we conducted a transcriptome analysis of flower samples from male, female and hermaphrodite plants using high-throughput SuperSAGE for digital gene expression analysis. Among the short sequence tags obtained from the transcripts, 312 unique tags were specifically mapped to the primitive sex chromosome (X or Yh) sequences. An annotation analysis revealed that retroelements are the most abundant sequences observed in the genes corresponding to these tags. The majority of tags on the sex chromosomes were located on the X chromosome, and only 30 tags were commonly mapped to both the X and Yh chromosome, implying a loss of many genes on the Yh chromosome. Nevertheless, candidate Yh chromosome-specific female determination genes, including a MADS-box gene, were identified. Information on these sex chromosome-specific expressed genes will help elucidating sex determination in the papaya.
To improve the efficiency of papaya anther culture, we investigated (1) hormonal medium conditions for inducing haploids or dihaploids; (2) identified the sex of established plantlets using a sex-specific DNA molecular marker and (3) estimated their ploidy by flow cytometry analysis of DNA content. Anthers with a mixture of uninucleate, mitotic, and binucleate microspores were collected from a male plant, and cultured on MS agar medium with different concentrations of CPPU and NAA. An embryo induction rate of 13.8% was attained on MS agar medium with 0.01 mg l −1 CPPU and 0.1 mg l −1 NAA. The induced embryos were subcultured on medium with 0.0025 mg l −1 CPPU. Rooting of the developed shoots was promoted by treating their basal parts with 1500 mg l −1 IBA in a 50% ethanol solution for about 10 seconds. All the embryo-derived plantlets (27 plants) were identified as female, implying that they were derived from microspores. In addition, 26 plants were determined to be triploids and one to be tetraploids. We also observed a wide range of morphological variation (e.g., in tree height and fruit size) among the established plants. Based on the results, we discussed a potential value of anther culture techniques for the breeding of papaya.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.