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Title: Involvement of facultative apomixis in inheritance of EPSPS gene amplification in glyphosate-resistant Amaranthus palmeri

Author
item RIBEIRO, DANIELA - Mississippi State University
item Pan, Zhiqiang - Peter
item Duke, Stephen
item Nandula, Vijay
item BALDWIN, BRIAN - Mississippi State University
item SHAW, DAVID - Mississippi State University
item Dayan, Franck

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2014
Publication Date: 2/4/2014
Citation: Ribeiro, D.N., Pan, Z., Duke, S.O., Nandula, V.K., Baldwin, B.S., Shaw, D.R., Dayan, F.E. 2014. Involvement of facultative apomixis in inheritance of EPSPS gene amplification in glyphosate-resistant Amaranthus palmeri. Planta. 239:199-212.

Interpretive Summary: Glyphosate is the most important herbicide in the world. Resistance to glyphosate has been slow to emerge but a number of weed species have now become resistant. Palmer amaranth (Amaranthus palmeri) has adapted to the presence of glyphosate by multiplying the number of copies of the gene encoding the enzyme inhibited by the herbicide. Our data shows that the inheritance of resistance is not straight forward. It appears that the offspring derived from resistant female plants were more resistant than the offspring derived from plants pollinated by resistant male plants. This paper reports that this may be due in part to the fact that female palmer amaranth plants can produce seeds without the normal process of sexual reproduction (a condition called apomixis). This process insures that, once it appears, resistance can persist in a population without pollination occurring.

Technical Abstract: The inheritance of glyphosate resistance in two Amaranthus palmeri populations (R1 and R2) was examined in reciprocal crosses (RC) and second reciprocal crosses (2RC) between glyphosate-resistant (R) and -susceptible (S) parents of this dioecious species. R populations and Female-R × Male-S crosses contain higher 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy numbers than the S population. EPSPS expression, EPSPS enzyme activity, EPSPS protein quantity, and level of resistance to glyphosate correlated positively with genomic EPSPS relative copy number. Transfer of resistance was more influenced by the female than the male parent in spite of the fact that the multiple copies of EPSPS are amplified in the nuclear genome. This led us to hypothesize that this perplexing pattern of inheritance may result from apomictic seed production in A. palmeri. We confirmed that reproductively isolated R and S female plants produced seeds, indicating that A. palmeri can produce seed both sexually and apomictically (facultative apomixis). This apomictic trait accounts for the low copy number inheritance in the Female-S × Male-R offsprings. Apomixis may also enhance the stability of the glyphosate resistance trait in the R populations in the absence of reproductive partners.