W552 Dynamic rearrangements and gene trafficking in nascent Yh chromosome of papaya

Date: Sunday, January 15, 2012
Time: 1:30 PM
Room: San Diego
Jianping Wang , University of Florida, Gainesville, FL
Jong-Kuk Na , Department of Agricultural Bio-resources, National Academy of Agricultural Science, Republic of Korea
Qingyi Yu , Texas A&M University, Weslaco, TX
Andrea Gschwend , University of Illinois at Urbana-Champaign, Urbana, IL
Paul H. Moore , Hawaii Agriculture Research Center
Jiming Jiang , University of Wisconsin-Madison, Madison, WI
Andrew Paterson , University of Georgia Plant Genome Mapping Lab, Athens, GA
Ray Ming , University of Illinois at Urbana - Champaign, Urbana, IL
Sex determination in papaya is controlled by a recently evolved XY chromosome pair, with two slightly different Y chromosomes, Y and Yh, respectively controlling development of males and hermaphrodites. The sequencing of the hermaphrodite-specific region of the Yh chromosome (HSY) and its X counterpart yielded an HSY pseudo-molecule of 8.1 megabases (Mb), and 3.5 Mb for the corresponding X region. The 131% expansion of the HSY is mostly due to retrotransposon insertions. The X region carries 81 genes, including 47 X/HSY gene pairs, and 34 genes present only in the X, which were apparently lost in the HSY. The HSY sequence includes 72 genes, of which 25 are HSY-specific. Ten HSY-specific genes were acquired from autosomes of which 3 were lost again, while the X region has acquired one. Sequence divergence between the alleles of retained X-HSY gene pairs reveals two evolutionary strata in the X chromosome, and the HSY differs from the X region by two large-scale inversions corresponding to the strata, causing recombination suppression. Numerous chromosomal rearrangements were detected within these inversions, and must have occurred later. The HSY’s expansion, rearrangements, and gene gains and losses, have occurred remarkably rapidly since this papaya chromosome region stopped recombining.