Page 133 - PC2019 Program & Proceedings

PLANT CANADA 2019

S51. mRNA long-distance transport of osmotic responsive genes in tomato/potato heterograft
1
2
1
*1
Hezema, Y. ; S. Sherif ; M. Shukla ; P. Saxena
1 University of Guelph
2 Virginia Tech
The mechanisms underlying the effect of the rootstock on the scion properties are largely unknown.
However, it has been established that the long-distance transport of mRNA through the graft union have a
vital effect on the properties of the scion. In the present study, we hypothesized that transcripts of some,
but not all, osmotic-responsive genes (ORGs) can be transported across the graft union, conferring
tolerance to the scion tissues. To test this hypothesis, we used a heterograft system with Solanum
tuberosum as the donor rootstock and Solanum lycopersicum as the recipient scion to identify transcripts
of some ORGs that move across the graft union under osmotic stress conditions. Reverse transcription–
PCR and quantitative real-time PCR analyses confirmed that among the studied ORGs, only NPR1
transcripts have been detected in the scion under normal and osmotic stress conditions. Our results also
indicated that the movement of mRNA is controlled by the need for the transported transcripts in the final
destination, rather than their abundance in the scion. As a salicylic acid receptor, NPR1 plays a key role in
abiotic and biotic stress tolerance, making it a plausible candidate for future transgrafting research. These
results may help us to get a clear understanding of the mechanisms underlying the systematic acquired
resistance in the tolerant grafted plants. Moreover, NPR1 can be used to produce transgenic tolerant
rootstocks.

Yasmine Hezema (yhezema@uoguelph.ca)

S52. Complex Regulation of Condensed Tannin Biosynthesis in Poplar by R2R3 MYB Activators
and Repressors
Constabel, P.
University of Victoria

Condensed tannins are widespread plant secondary metabolites and highly abundant in woody plants. In
poplar, condensed tannin biosynthesis responds to environmental stimuli, and is induced by wounding,
pathogen infection, UV-B, high light stress, and nitrogen deficiency. CT synthesis is controlled by several
R2R3 MYB transcription factor, including both positive and negative regulators. In particular, the
MYB134 and MYB115 are key activators, and when overexpressed in transgenic poplars, lead to a strong
over-accumulation of CTs. Surprisingly, these activator MYBs simultaneously induce expression of
R2R3 MYB repressors, which we have shown can downregulate the CT pathway. Transcriptomic
analysis of both MYB activator- and MYB repressor-overexpressing transgenics have provided new
potential target genes and pathways. Our recent work attempts to determine how these regulators
cooperate during stress induction of CTs. Promoter activation assays in poplar cells demonstrate that
flavonoid genes are the targets of activator MYBs, and that this activation can be inhibited by the
repressors. Furthermore, the MYB115 and MYB134 activators also regulate each other and a bHLH co-
factor gene. Our data indicates that stress-induction of CTs in poplar depends on a complex network of
positive and negative regulators, which act to fine-tune CT biosynthesis. How these genes are controlled
by environmental stress will be investigated in future work.

Peter Constabel (cpc@uvic.ca)

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