Submitted to: Nature
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/19/2003
Publication Date: 1/22/2004
Citation: Liu, Z., Moore, P.H., Ma, H., Ackerman, C.M., Ragiba, M., Yu, Q., Pearl, H.M., Kim, M.S., Charlton, J.W., Stiles, J.I., Zee, F.T., Paterson, A.H., Ming, R. 2004. A primitive y chromosome in papaya marks incipient sex chromosomes evolution. Nature 427: 348-352. 2004 Interpretive Summary: Public interest in the evolution and function of the human male sex chromosome was piqued by the June 19 Nature special issue detailing sex chromosome DNA sequences. Contrasted with the sex chromosomes of mammals, those of plants have evolved separately in many families and are poorly characterized. We report findings that, in contrast to the roughly 240-320 million year age of human sex chromosomes and their antecedents, the papaya plant's recently evolved sex-determination system appears to be at the dawn of sex chromosome evolution. Parallels in the evolution of sex chromosomes in plants and animals are illustrated in that the primitive sex chromosomes in papaya share characteristics that are typical of well developed mammalian sex chromosomes, including suppression of recombination and degeneration of the male sex Y chromosome (MSY) region, as driving forces in sex chromosome evolution. Genomic analyses of papaya's primitive MSY provide direct evidence that sex chromosomes are evolving from autosomes as predicted by evolutionary biology theory. This direct evidence of a decades old hypothesis has potential for revealing details into the beginning stages of sex chromosome evolution.
Technical Abstract: Eukaryotic sex chromosomes are believed to have evolved from ancestral autosomes. Genetic analyses indicate that sex chromosomes in higher plants have evolved recently and independently in several taxa. A papaya chromosome which contains a male-specific locus shows much recombination suppression and DNA sequence degeneration in the male-specific region (MSY) that accounts for about 10% of the chromosome. Sequence duplications and transposable element insertions may have contributed to degeneration of the MSY on the primitive Y chromosome resulting in low gene density. This finding provides direct evidence for the origin of sex chromosomes from autosomes.