Abstract Detail

Systematics Section/ASPT

Nicolas, Antoine [1], Plunkett, Gregory [2].

Implications of RPB2 Duplications on the Evolution of Apiales.

The gene for the second largest subunit of DNA-dependent RNA polymerase II (RPB2) was studied to estimate phylogenetic relationships in the eudicot order Apiales. A region from exon 18 to exon 23 (including introns) was sequenced from c. 300 species representing all major clades of Apiales. Based on interpretations from parsimony and maximum likelihood analyses, at least two copies of RPB2 could be identified in most lineages, representing at least five independent duplication events in the order. Except for some Araliaceae, no significant differences were found in the evolutionary rates between the two copies in most clades. Also, neither of the two copies is under positive selection but they are more likely to be under purifying selection. Comparisons of amino acid clusters indicate that there is no heterogeneity in function among the duplicates. All copies appear to be functional but may have undergone subfunctionalization. The orthologous and paralogous copies of RPB2 provide a rich source of information for understanding the evolutionary history of Apiales, especially in clades of polyploid origin. In Araliaceae, for example, several independent duplication events are specific to clades having many known polyploid species, suggesting an ancient allopolyploid origin of entire clades. The oldest duplications can be mapped to the early history of Apiales (c. 100 Mya) and appears to precede the divergence of the four families of suborder Apiineae (Apiaceae, Araliaceae, Myodocarpaceae, and Pittosporaceae). Both copies place Pittosporaceae as the earliest diverging lineage in the suborder, followed by Araliaceae, and then Myodocarpaceae and Apiaceae. Two duplication events are evident in Apiaceae. One is shared between subfamilies Apioideae and Saniculoideae. The other is limited to the Azorella clade of subfamily Azorelloideae and represents the most recent duplication in Apiineae (c. 50 Mya). Both copies demonstrate the polyphyly of Azorella, the largest genus in Azorelloideae, and the role of rapid radiation and reticulation in shaping the history of that subfamily. Beyond Apiineae, duplicate copies of RPB2 were detected in the early-diverging families Griseliniaceae and Pennantiaceae, but these appear to be more recent than the earliest duplication found in Apiineae.

Broader Impacts:

1 - New York Botanical Garden, Institute of Systematic Botany, 2900 Southern Blvd., Bronx, NY, 10458-5126, USA
2 - New York Botanical Garden, Cullman Program For Molecular Systematics, 2900 Southern Blvd., Bronx, NY, 10458-5126, USA

Keywords:
RPB2
Paralogy
gene duplication
Apiales
Allopolyploids.

Presentation Type: Oral Paper:Papers for Sections
Session: 33
Location: Rosedown/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 2:30 PM
Number: 33005
Abstract ID:824
Candidate for Awards:None