35th NPS abstract book

P37
Unraveling the polyploid origin of coast redwood (Sequoia sempervirens)
with Bayesian concordance analysis
A. D. SCOTT, N. STENZ and D. A. BAUM
Department of Botany, University of Wisconsin - Madison, 430 Lincoln Drive, Madison, WI 53706,
USA
Coast redwood (Sequoia sempervirens) stands out as not only one of the tallest, longest-lived trees,
but as the only hexaploid conifer. As whole genome duplication is rare in gymnosperms, a better
understanding of the causes of polyploidy in Sequoia may clarify why polyploidy has played a
relatively minimal role in gymnosperm evolution. We sequenced transcriptomes from Sequoia,
Sequoiadendron, and Metasequoia, and estimated phylogenetic trees for 3,605 genes. Bayesian
concordance analysis of 3,045 low-copy genes suggests Sequoiadendron is the closest relative of
Sequoia for ~80% of the genome. Gene trees with multiple homeologs in coast redwood consistently
show monophyly of those homeologs. This suggests that hexaploidy is a result of autopolyploidy or,
that if hybridization did occur, it involved only species that are more closely related to Sequoia than
either Sequoiadendron or Metasequoia. Our analyses suggest a polyploid origin for Sequoia ~24 mya
(homeolog divergence at K s ~ 0.0168), in apparent contradiction to the fossil record.
P38
Who’s who? Finding the CESA genes in White Spruce encoding the secondary
wall specific cellulose synthase
I. DUVAL 1 , D. LACHANCE 1 , I. GIGUÈRE 2 , M-J. MORENCY 1 , G. PELLETIER 1 , J. J. MACKAY 2, 3 and A.
SÉGUIN 1*
1 Natural Resources Canada, Laurentian Forestry Centre, Québec QC G1V 4C7, Canada; 2 Centre
d’Étude de la Forêt, Université Laval, Québec (QC), G1V A06, Canada; 3 Department of Plant Sciences,
University of Oxford, Oxford, OX1 2RB, UK
Phylogenetic analyses of CESA genes have shown specific divergence within the gene family for
either primary or secondary wall development. In Picea glauca (white spruce) the PgCESA3 gene has
been principally associated to developing xylem. Tissue specific gene expression analyses using a
PgCESA3 promoter-GUS reporter construct revealed localised expression associated to secondary
wall formation. We also obtained evidences that specific spruce MYB transcription factors are
implicated in the regulation of PgCESA3 gene promoter by using a tissue culture based system and a
transactivation approach. Furthermore, using electrophoretic mobility shift assay (EMSA) we
confirmed that PgMYB12 directly binds in vitro to the PgCESA3 promoter. Overall, functional
genomic tools and global expression data for white spruce is a powerful assets for delineating the
evolution and dynamics of complex gene families such as CESA.
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