Multiple target site resistance to glyphosate in junglerice (Echinochloa colona) lines from California orchards

Abstract

These results indicate that an altered target site in EPSPS is contributing to resistance in these lines and resistance has evolved independently, multiple times in the Central Valley of California. Additional research is needed to further understand the genomic contributions of resistance loci in this polyploid weed species. © 2018 Society of Chemical Industry.

Do plants pay a fitness cost to be resistant to glyphosate?

“…A number of engineered and natural bacterial and plant EPSPS variants have been shown to prevent glyphosate binding and thus endow glyphosate resistance (Healy‐Fried et al ., ; Alibhai et al ., ; Sammons & Gaines, ; Yi et al ., ; Sammons et al ., ). Since the first identification of a naturally evolved glyphosate resistance EPSPS gene mutation, resulting in a Pro‐106‐Ser substitution in Eleusine indica (Baerson et al ., ), other single amino acid substitutions (Thr, Ala, Leu) at the same Pro‐106 residue have been reported to endow glyphosate resistance in weed species (Ng et al ., ; Yu et al ., ; Kaundun et al ., ; Sammons & Gaines, ; Morran et al ., ). Artificial and naturally evolved double EPSPS gene mutations have also been reported to confer glyphosate resistance in bacteria and plants (Padgette et al ., ; Kahrizi et al ., ; Funke et al ., ; Sammons & Gaines, ; Chen et al ., , ; Yu et al ., ).…”

“…As outlined earlier, glyphosate resistance‐endowing amino acid substitutions at Pro‐106 lead only to low‐level glyphosate resistance and a lack of significant changes in EPSPS functionality (Table ). Not surprisingly, Pro‐106 substitutions are the most common form of target‐site glyphosate resistance (Powles & Yu, ; Sammons & Gaines, ; Morran et al ., ), and resistant individuals show no fitness cost at the plant level, and persist in populations in the absence of glyphosate selection (Yu et al ., ; Fernández‐Moreno et al ., ; Han et al ., ; Wu et al ., ).…”

“…Additionally, a recently reported novel resistance mechanism involves rapid tissue necrosis by as‐yet‐unknown mechanisms that limit glyphosate transport in resistant Ambrosia trifida (Moretti et al ., ). It is important to realize that both target‐ and nontarget‐site glyphosate resistance mechanisms can coexist within an individual plant and within plant populations (Bostamam et al ., ; Morran et al ., ). Thus, individual plants and/or populations can express both different target‐site (e.g.…”

EPSPS duplication and mutation involved in glyphosate resistance in the allotetraploid weed species Poa annua L.

“…Because glyphosate inhibits EPSPS, an enzyme of the shikimic acid pathway involved in the catalysis of the reaction between shikimate-3-phosphate and P-enolpyruvate, shikimic acid accumulates as a result of this inhibition and may be used as a biomarker to quantify glyphosate activity in plants. The accumulation of shikimic acid in response to glyphosate was measured as described by Morran et al 16 and based on methods by Shaner 26 with modifications. Briefly, seedlings were treated at the threeto four-leaf stage with 0, 435 and 870 g a.e ha −1 of glyphosate (Roundup PowerMAX ® ) as previously described.…”

“…Single nucleotide substitutions (SNPs) in EPSPS, identified in several weed species, result in a wide range of glyphosate resistance levels depending on the species. 15,16 SNPs that are commonly involved in glyphosate resistance are reported to occur at position 106 of the EPSPS, where a proline (wild-type) may be substituted by an alanine, leucine, serine or threonine. 17 Double mutations in the EPSPS (at coding positions 102 and 106) have been described in transgenic crops and weeds, increasing even further the level of glyphosate resistance.…”