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Abstract Detail


Evolutionary Developmental Biology (Evo-Devo)

Hearn, David [1], Poulsen, Travis [1].

Parallel evolutionary origins of storage woods in roots and shoots of Brassica: evidence from RNA-Seq.

Wood is a key evolutionary innovation that carries out three primary functions in vascular plants:mechanical support, water conduction, and storage. Multiple different anatomical strategies have evolved that emphasize one or more of these functions over the others. Parenchymatous woods, that include the succulent woods of many xeric-adapted species, are woods dominated by the storage function. Previous work suggests that parenchymatous woods evolved in well over 30 families in roots and shoots. Many of these separate evolutionary origins are associated with the concomitant evolution of medullary, axial, or cortical bundles in a matrix of proliferating parenchyma. Highly parenchymatized woods evolved on at least three occasions in the genus Brassica (turnip and rutabaga root / hypocotyl, kohlrabi shoot). We investigated the anatomy of these parenchymatous woods and performed a comparative transcriptomics analysis using RNA-Seq approaches. We compared the genome-wide mRNA transcript abundances between stems of (1) kohlrabi (B. oleracea gongylodes "express forcer" stem storage) and kale (B. oleracea acephala "white crane" thin / lignified woods) and between roots / hypocotyls / lower stems of (2) turnip (B. rapa rapa "Tokyo hybrid" root / hypocotyl storage) and bak choi (B. rapa chinensis thin / lignified roots / hypocotyls) to identify gene candidates responsible for developmental and evolutionary transitions between the putatively ancestral condition - lignified woods - of bak choi and kale and the derived parenchymatous woods of turnip and kohlrabi. Similar to other distantly related groups with parenchymatous woods, we find that both kohlrabi and turnips have some proliferation of parenchyma and (amphivasal) vascular bundles in their storage organs; these features are lacking in the stems and roots of kale and bak choi. Further, there is a statistically significant overlap (p-value < 10e-7) between the two sets of differentially expressed genes identified through the comparisons between(1) kohlrabi and kale or between (2) turnip and bak choi. Despite separate evolutionary origins of the storage structures of kohlrabi and turnip, these results suggest a significant overlap in the genetic machinery responsible for the development of storage organs, indicating parallel evolutionary origins of parenchymatous woods in roots and shoots of these taxa.

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Keywords:
Brassica
parallel evolution
succulence
RNA-seq
parenchymatous wood
differential gene expression.

Presentation Type: Oral Paper:Papers for Topics
Session: 22
Location: Delaware C/Hyatt
Date: Tuesday, July 10th, 2012
Time: 8:00 AM
Number: 22001
Abstract ID:911


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