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Title: Reduced expression of defense-related transcripts of an invasive weed in its introduced range

Author
item BROZ, AMANDA - CO ST U, FT. COLLINS, CO
item Manter, Daniel
item BOWMAN, GILLIANNE - FRIBOURG, SWITZERLAND
item MULLER-SCHARER, HENIZ - FRIBOURG, SWITZERLAND
item VIVANCO, JORGE - CO ST U, FT. COLLINS, CO

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2009
Publication Date: 3/23/2009
Citation: Broz, A., Manter, D.K., Bowman, G., Muller-Scharer, H., Vivanco, J. 2009. Reduced expression of defense-related transcripts of an invasive weed in its introduced range. Biomed Central (BMC) Plant Biology. 9:33.

Interpretive Summary: Ecological and physiological studies have thus far provided an incomplete picture of why some plants become invasive; therefore we used genomic resources to complement and advance this field. The evolution of increased competitive ability (EICA) hypothesis predicts that in the introduced range invaders rapidly evolve to put fewer resources into defense and more resources into growth and/or fecundity compared to plants in the native range, a phenomenon which can potentially be studied at the level of gene expression. Using sequence information from the invasive plant spotted knapweed, Centaurea maculosa, we characterized and compared expression of candidate genes that may be involved in constitutive defense or rapid evolution between native (Eurasian) and invasive (North American) populations of greenhouse grown C. maculosa plants. We found evidence that invasive populations had reduced expression of defense and secondary metabolism-related transcripts in comparison to their native tetraploid counterparts, as might be expected based on EICA. Measurements of several vegetative and reproductive traits were similar for all plant populations, contrary to the expectations of EICA; however, invasive populations had significantly greater survival rates following flowering and a simulation of seed production suggests that invasive tetraploids have the greatest reproductive capacity of the three geo-cytotypes. Ploidy also had a significant effect on gene expression, such that expression levels for four of the ten total genes examined were significantly lower for native diploid as compared to native tetraploid populations. Our results suggest that characterizing gene expression in an invasive species using populations from both its native and introduced range can provide insight into the biology of plant invasion that may not be revealed by traditional measurements of plant performance.

Technical Abstract: Ecological and physiological studies have thus far provided an incomplete picture of why some plants become invasive; therefore we used genomic resources to complement and advance this field. The evolution of increased competitive ability (EICA) hypothesis predicts that in the introduced range invaders rapidly evolve to put fewer resources into defense and more resources into growth and/or fecundity compared to plants in the native range, a phenomenon which can potentially be studied at the level of gene expression. Using sequence information from the invasive plant spotted knapweed, Centaurea maculosa, we characterized and compared expression of candidate genes that may be involved in constitutive defense or rapid evolution between native (Eurasian) and invasive (North American) populations of greenhouse grown C. maculosa plants. We found evidence that invasive populations had reduced expression of defense and secondary metabolism-related transcripts in comparison to their native tetraploid counterparts, as might be expected based on EICA. Measurements of several vegetative and reproductive traits were similar for all plant populations, contrary to the expectations of EICA; however, invasive populations had significantly greater survival rates following flowering and a simulation of seed production suggests that invasive tetraploids have the greatest reproductive capacity of the three geo-cytotypes. Ploidy also had a significant effect on gene expression, such that expression levels for four of the ten total genes examined were significantly lower for native diploid as compared to native tetraploid populations. Our results suggest that characterizing gene expression in an invasive species using populations from both its native and introduced range can provide insight into the biology of plant invasion that may not be revealed by traditional measurements of plant performance.