Page 144 - PC2019 Program & Proceedings

PLANT CANADA 2019

S73. De novo assembly of the pokeweed genome provides insight into pokeweed antiviral protein
(PAP) gene expression
*1
1
Neller, K. ; C. Diaz ; A. Platts ; K. Hudak 1
2
1 York University
2 New York University
Pokeweed antiviral protein (PAP) is a ribosome-inactivating protein synthesized by American pokeweed
(Phytolacca americana). PAP inhibits virus infection when expressed in crop plants, yet little is known
about the function of PAP in pokeweed due to a lack of genomic tools for this non-model species. We de
novo assembled the pokeweed genome from short-read sequencing and annotated protein-coding genes.
Our draft assembly (83X coverage, N50 = 42.5 Kb) accounted for 74% of the measured pokeweed
genome size of 1.3 Gb. We obtained 29,773 genes, 73% of which contained known protein domains, and
identified several PAP isoforms. Within the gene models of each PAP isoform, a long 5’ UTR intron was
discovered and validated by PCR and RT-PCR. Interestingly, the intron stimulated reporter gene
expression in tobacco. We complemented this genomic resource with expression profiles of pokeweed
plants subjected to stress treatments (JA, SA, PEG, and wounding; n=4). Cluster analysis revealed that
some PAP isoforms were co-expressed with genes involved in terpenoid biosynthesis, JA-mediated
signalling, and metabolism of amino acids and carbohydrates. Diverse, stress-responsive cis-regulatory
elements were present in PAP isoform promoters, and we identified a region of PAP-I sufficient for JA
response in tobacco, based on reporter constructs containing promoter truncations. This study generated
the first draft genome for the Phytolaccaceae family and provided insight into the regulation and function
of PAP in pokeweed.

Kira Neller (nellerk@yorku.ca)

S74. The long story of small RNA: sRNA architecture of Brassica napus seed development
*
Ziegler, D. ; D. Khan; M. Belmonte
University of Manitoba

Canola (Brassica napus L.) is a nascent allotetraploid and is Canada’s most important oilseed crop,
contributing $26.7 billion to the Canadian economy in 2016. Despite this, seed development in B. napus
is not well understood, especially from an epigenetic perspective. Seed development in eudicots is
preceded by the ovule stage (pre-fertilization) and followed by morphogenesis and maturation phases
constituting embryo development. Morphogenesis is defined by cellular differentiation and tissue
organization of the embryo, while elongation and deposition of lipids/proteins are characteristic of
maturation in late seed development. Small RNAs (sRNA) act as important genetic switches in
orchestrating developmental processes and are particularly important in regulating gene activity during
precise developmental transitions. Broadly, small RNAs can be classified into two groups: micro RNA
(miRNA) and small interfering RNA (siRNA). While siRNA and miRNAs both act as negative regulators
of gene expression, their modes of biogenesis and loci encoding them vary drastically among subgroups.
In this work, we predict the sRNA populations of five stages of seed development and dissect the
different miRNA and siRNA profiles between them. We find siRNA populations to be much more
diverse than that of miRNAs, and that subgenome dominance is evident throughout seed development.
Lastly, we predict targets of the sRNAs to extrapolate biological function, and piece together the
epigenetic machinery underpinning B. napus seed development.

Dylan Ziegler (Dylan.ziegler@umanitoba.ca)

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