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Title: Recent Origin of the Papaya Sex Chromosomes

Author
item YU, QINGYI
item HOU, SHAOBIN
item FELTUS, ALEX
item MOORE, RICHARD
item Moore, Paul
item ALAM, MAQSUDUL
item JIANG, JIMING
item PATERSON, ANDREW
item MING, RAY

Submitted to: Microbial Pathogensis and Host Response: Cold Spring Harbor Laboratory
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2007
Publication Date: 3/1/2007
Citation: Yu, Q., Hou, S., Feltus, A., Moore, R.C., Moore, P.H., Alam, M., Jiang, J., Paterson, A., Ming, R. 2007. Recent Origin of the Papaya Sex Chromosomes. Cold Spring Harbor Laboratory.

Interpretive Summary: not applicable

Technical Abstract: Sex chromosomes in flowering plants, in contrast to those in animals, evolved relatively recently and only a few are heteromorphic. The sex chromosomes of papaya appear at the cytological level to be homomorphic but, at the molecular level, we are finding that the papaya Y chromosome shows features of incipient sex chromosome evolution. To survey the state of the hermaphrodite Y (Yh) chromosome differentiation, we sequenced two pairs of X and Yh specific bacterial artificial chromosomes (BACs) and conducted functional analysis on two X BACs and seven Yh BACs. Sequence comparison between the two paired X and Yh BACs revealed three inversion events on the MSY. Aligning the paired BAC sequences showed that one of the Yh BACs had expanded by 9.6% and the other Y BAC had expanded by 35.2%. One gene on the Yh chromosome might have been lost by deletion, while its corresponding gene on the X chromosome is still functional. Analysis of sequence divergence between five X and Yh gene pairs indicates that they are functionally constrained, which is a characteristic of young sex chromosomes. Our estimate of the age of divergence between X-Y gene pairs ranges from 1.3-2.8 million years ago, supporting a recent origin of the primitive sex chromosomes in papaya.