Abstract Detail

Developmental and Structural Section

Hearn, David [1], Krosnick, Shawn [2].

Comparative transcriptomics of extrafloral nectaries: a search for homology.

Extrafloral nectaries are glands that produce carbohydrate and amino acid-rich secretions. These secretions attract animals that are known to defend the host plant against herbivores. More recently, they were also recognized to contribute to species diversification in select lineages. EFNs evolved in more than 20 plant families, and within clades possessing EFNs, they exhibit a diversity of morphologies and positions on leaves and other structures outside of flowers. Despite their ecological importance, their role in contributing to diversification, and their structural and functional diversity, very few studies have examined the molecular bases for this diversity. Our research therefore addressed two questions. First, are the same genes recruited during separate evolutionary origins of EFNs? Second, which gene orthologs are co-recruited, and which genes carry out specialized roles during the evolution of EFNs in different plant taxa? We took a comparative RNA-Seq transcriptomics approach to detect changes in gene expression, genome wide, between leaf tissues with EFNs and leaf tissues lacking EFNS from two taxa (Adenia hastata, and Passiflora morifolia) that represent separate evolutionary origins of EFNs. EFNs are on petiolar projections in P. morifolia, whereas they are present on contorted membranes at the leaf apex of A. hastata, so EFNs are morphologically distinct as well. Following RNA-Seq de novo assembly and expression level quantitation, we carried out multiple downstream analyses to address our focal questions including functional annotation and mapping of orthology between transcripts of the two species. Based on this assessment of orthology, we found that there was a statistically significant overlap of 50 ortholog clusters (hypergeometric exact test p-value< 1e-10) that were differentially expressed (DE) in the A. hastata tissues and the P. morifolia tissues possessing EFNs. Both sets of DE genes in A. hastata and in P. morifolia were functionally enriched in gene ontology terms related to development (e.g. auxin biosynthetic process, gibberellin mediated signaling pathway, organ boundary specification, transcription factor activities), coloration (positive regulation of anthocyanin metabolic process), and starch biosynthesis. Despite this overlap in differentially expressed genes and their functions, there were several hundred orthologs that were uniquely DE in EFNS of either A. hastata or, vice versa, in P. morifolia alone. Collectively, these results suggest that a core set of orthologs are co-recruited during the evolution of EFNs in separate lineages, but distinct genes in each lineage are likely to be responsible for EFN specialization in position, morphology, and function.

1 - Towson University, 8000 York Road, Towson, MD, 21252, USA
2 - Tennessee Technological University, Biology, 1100 North Dixie, Pennebaker Hall 207, Cookeville, TN, 38501, United States

Keywords:
extrafloral nectary
homology
RNA-Seq
Passiflora
Adenia.

Presentation Type: Oral Paper:Papers for Sections
Session: 69
Location: Salon 11/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 2:45 PM
Number: 69006
Abstract ID:996
Candidate for Awards:None