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Abstract Detail

Comparative Genomics/Transcriptomics

Maynord, Silas [1], Krosnick, Shawn [2], Hearn, David [3].

Differential Gene Expression as a Tool for Assessing Homology among Extrafloral Nectaries in Passiflora L. (Passifloraceae).

Extrafloral nectaries (EFNs) are sugar-producing structures that provide rewards for insects in exchange for defense against herbivory. These structures are remarkably diverse across angiosperms, evolving independently in many lineages. Passifloraceae, known as the passionflowers, is an excellent lineage within which to study the evolution of EFNs due to high morphological diversity, unique distributional patterns, and genetic proximity. One question of particular interest involves the identification of precursor structures for EFNs in Passifloraceae. This family belongs to the salicoid lineage, which exhibits both secretory leaf teeth and EFNs, suggesting that there may be homology at a genetic level among these structures. A comparative transcriptomic study identified 12 genes with significant differential expression in EFN structures using one species of Passiflora and one species of Adenia. In the present study, gene expression patterns in four of these candidate genes, SHI, B3-1, B3-2, and NAC are examined in Passiflora morifolia, P. incarnata, and P. boenderi. Real-time qPCR was utilized to examine differential expression within each candidate gene at early developmental stages of EFN, non-EFN, and leaf teeth tissue. Results indicate the upregulation of SHI in all EFN and marginal teeth tissue for the three species. However, B3-1, B3-2, and NAC show unique patterns of expression when examined across the three species. For B3-1 and B3-2, Passiflora morifolia and P. incarnata petiole EFNs exhibit upregulation, but abaxial laminar nectaries in P. boenderi do not, instead showing greater expression in the lamina. These two genes may have secondary roles in margin development rather than EFNs specifically. For NAC, gene expression is less specific to EFN tissue in the lamina of P. boenderi and the petiole of P. incarnata, but expression is still higher in leaf teeth. These patterns suggest that NAC may have a secondary role in lamina and petiole development. The present data suggest similar genetic mechanisms may be involved in the formation of leaf teeth and EFNs in Passiflora, at least with respect to SHI. Additional candidate genes identified will be evaluated for their role in future studies.

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1 - Tennessee Technological University, Department of Biology, 1100 North Dixie Avenue, Pennebaker Hall #207, Cookeville, Tennessee, 38505, USA
2 - Tennessee Tech University, Dept. Of Biology, 1100 North Dixie Avenue, Pennebaker Hall #207, Cookeville, TN, 38505, United States
3 - Towson University, Biology, 8000 York Road, Towson, MD, 21252, USA

Extrafloral Nectaries

Presentation Type: Oral Paper
Session: CG1, Comparative Genetics/Genomics I
Location: Tucson I/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 11:30 AM
Number: CG1012
Abstract ID:704
Candidate for Awards:None

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