Ectopic expression of a rice triketone dioxygenase gene confers mesotrione tolerance in soybean

BACKGROUND

Herbicide-resistant weeds pose a challenge to agriculture and food production. New herbicide tolerance traits in crops will provide farmers with more options to effectively manage weeds. Mesotrione, a selective pre- and post-emergent triketone herbicide used in corn production, controls broadleaf and some annual grass weeds via hydroxyphenylpyruvate dioxygenase (HPPD) inhibition. Recently, the rice HIS1 gene, responsible for native tolerance to the selective triketone herbicide benzobicyclon, was identified. Expression of HIS1 also confers a modest level of mesotrione resistance in rice. Here we report the use of the HIS1 gene to develop a mesotrione tolerance trait in soybean.

RESULTS

Conventional soybean is highly sensitive to mesotrione. Ectopic expression of a codon-optimized version of the rice HIS1 gene (TDO) in soybean confers a commercial level of mesotrione tolerance. In TDO transgenic soybean plants, mesotrione is rapidly and locally oxidized into noninhibitory metabolites in leaf tissues directly exposed to the herbicide. These metabolites are further converted into compounds similar to known classes of plant secondary metabolites. This rapid metabolism prevents movement of mesotrione from treated leaves into vulnerable emerging leaves. Minimizing the accumulation of the herbicide in vulnerable emerging leaves protects the function of HPPD and carotenoid biosynthesis more generally while providing tolerance to mesotrione.

CONCLUSIONS

Mesotrione has a favorable environmental and toxicological profile. The TDO-mediated soybean mesotrione tolerance trait described here provides farmers with a new option to effectively manage difficult-to-control weeds using familiar herbicide chemistry. This trait can also be adapted to other mesotrione-sensitive crops (e.g. cotton) for effective weed management. © 2022 Bayer Crop Science. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Microbial HemG-type protoporphyrinogen IX oxidase enzymes for biotechnology applications in plant herbicide tolerance traits

BACKGROUND

Protoporphyrinogen IX oxidase (PPO)-inhibiting herbicides act by inhibiting a key enzyme in the heme and chlorophyll biosynthetic pathways in plants. This enzyme, the PPO enzyme, is conserved across plant species. However, some microbes are known to utilize a unique family of PPO enzymes, the HemG family. This enzyme family carries out the same enzymatic step as the plant PPO enzymes, but does not share sequence homology with the plant PPO enzymes.

RESULTS

Bioinformatic analysis was used to identify putative HemG PPO enzyme variants from microbial sources. A subset of these variants was cloned and characterized. HemG PPO variants were characterized for functionality and tolerance to PPO-inhibiting herbicides. HemG PPO variants that exhibited insensitivity to PPO-inhibiting herbicides were identified for further characterization. Expression of selected variants in maize, soybean, cotton and canola resulted in plants that displayed tolerance to applications of PPO-inhibiting herbicides.

CONCLUSION

Selected microbial-sourced HemG PPO enzyme variants present an opportunity for building new herbicide tolerance biotechnology traits. These traits provide tolerance to PPO-inhibiting herbicides and, therefore, could provide additional tools for farmers to employ in their weed management systems. © 2019 Society of Chemical Industry.

Development of enzymes for robust aryloxyphenoxypropionate and synthetic auxin herbicide tolerance traits in maize and soybean crops

BACKGROUND

Effective management of weedy species in agricultural fields is essential for maintaining favorable growing conditions and crop yields. The introduction of genetically modified crops containing herbicide tolerance traits has been a successful additional tool available to farmers to better control weeds. However, weed resistance challenges present a need for additional herbicide tolerance trait options.

RESULTS

To help meet this challenge, a new trait that provides tolerance to an aryloxyphenoxypropionate (FOP) herbicide and members of the synthetic auxin herbicide family, such as 2,4-dichlorophenoxyacetic acid (2,4-D), was developed. Development of this herbicide tolerance trait employed an enzyme engineered with robust and specific enzymatic activity for these two herbicide families. This engineering effort utilized a microbial-sourced dioxygenase scaffold to generate variants with improved enzymatic parameters. Additional optimization to enhance in-plant stability of the enzyme enabled an efficacious trait that can withstand the higher temperature conditions often found in field environments.

CONCLUSION

Optimized herbicide tolerance enzyme variants with enhanced enzymatic and temperature stability parameters enabled robust herbicide tolerance for two herbicide families in transgenic maize and soybeans. This herbicide tolerance trait for FOP and synthetic auxin herbicides such as 2,4-D could be useful in weed management systems, providing additional tools for farmers to control weeds. © 2019 Society of Chemical Industry.

Lysine acetylation is a widespread protein modification for diverse proteins in Arabidopsis

Lysine acetylation (LysAc), a form of reversible protein posttranslational modification previously known only for histone regulation in plants, is shown to be widespread in Arabidopsis (Arabidopsis thaliana). Sixty-four Lys modification sites were identified on 57 proteins, which operate in a wide variety of pathways/processes and are located in various cellular compartments. A number of photosynthesis-related proteins are among this group of LysAc proteins, including photosystem II (PSII) subunits, light-harvesting chlorophyll a/b-binding proteins (LHCb), Rubisco large and small subunits, and chloroplastic ATP synthase (β-subunit). Using two-dimensional native green/sodium dodecyl sulfate gels, the loosely PSII-bound LHCb was separated from the LHCb that is tightly bound to PSII and shown to have substantially higher level of LysAc, implying that LysAc may play a role in distributing the LHCb complexes. Several potential LysAc sites were identified on eukaryotic elongation factor-1A (eEF-1A) by liquid chromatography/mass spectrometry and using sequence- and modification-specific antibodies the acetylation of Lys-227 and Lys-306 was established. Lys-306 is contained within a predicted calmodulin-binding sequence and acetylation of Lys-306 strongly inhibited the interactions of eEF-1A synthetic peptides with calmodulin recombinant proteins in vitro. These results suggest that LysAc of eEF-1A may directly affect regulatory properties and localization of the protein within the cell. Overall, these findings reveal the possibility that reversible LysAc may be an important and previously unknown regulatory mechanism of a large number of nonhistone proteins affecting a wide range of pathways and processes in Arabidopsis and likely in all plants.

Decrease in leaf sucrose synthesis leads to increased leaf starch turnover and decreased RuBP regeneration-limited photosynthesis but not Rubisco-limited photosynthesis in Arabidopsis null mutants of SPSA1

We investigated the individual effect of null mutations of each of the four sucrose-phosphate synthase (SPS) genes in Arabidopsis (SPSA1, SPSA2, SPSB and SPSC) on photosynthesis and carbon partitioning. Null mutants spsa1 and spsc led to decreases in maximum SPS activity in leaves by 80 and 13%, respectively, whereas null mutants spsa2 and spsb had no significant effect. Consistently, isoform-specific antibodies detected only the SPSA1 and SPSC proteins in leaf extracts. Leaf photosynthesis at ambient [CO₂] was not different among the genotypes but was 20% lower in spsa1 mutants when measured under saturating [CO₂] levels. Carbon partitioning at ambient [CO₂] was altered only in the spsa1 null mutant. Cold treatment of plants (4 °C for 96 h) increased leaf soluble sugars and starch and increased the leaf content of SPSA1 and SPSC proteins twofold to threefold, and of the four null mutants, only spsa1 reduced leaf non-structural carbohydrate accumulation in response to cold treatment. It is concluded that SPSA1 plays a major role in photosynthetic sucrose synthesis in Arabidopsis leaves, and decreases in leaf SPS activity lead to increased starch synthesis and starch turnover and decreased Ribulose 1,5-bisphosphate regeneration-limited photosynthesis but not ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco)-limited photosynthesis, indicating a limitation of triose-phosphate utilization (TPU).

Genetic interactions between the miRNA164-CUC2 regulatory module and BREVIPEDICELLUS in Arabidopsis developmental patterning

The proper regulation of enlargement and patterning of plant lateral organs is essential for plant functionality. In an earlier work, we characterized the role of a microRNA (miRNA)-transcription factor regulatory module, miRNA164-CUC2, in the enlargement and patterning of multiple lateral organs in Arabidopsis. This regulatory module genetically interacts with another transcription factor, CRC, in fruit development patterning. Here, we characterize the genetic interaction of this module with a homeodomain transcription factor, BREVIPEDICELLUS (BP), that has been shown to play roles in leaf development patterning.

A microRNA-transcription factor module regulates lateral organ size and patterning in Arabidopsis

Precise regulatory mechanisms are necessary to properly control the enlargement and patterning of plant lateral organs. However, our understanding of the regulatory modules that govern both of these processes is limited. An emerging theme in plant development is microRNA (miRNA)-mediated gene regulation of transcription factors, including several NAC domain family members such as CUP-SHAPED COTYLEDON2 (CUC2). We uncovered a novel allele of CUC2, cuc2-1D, that revealed important functions of miRNAs and CUC2 in a regulatory module governing lateral organ enlargement and patterning. cuc2-1D carried a single point mutation in the CUC2 miRNA target site, disrupting miRNA targeting. Disruption of the tight balance between CUC2 and its targeting miRNA, miRNA164, led to over-accumulation of CUC2 mRNA and expansion of the CUC2 expression domain. cuc2-1D plants had enlarged vegetative and reproductive lateral organs relative to wild-type plants. Mechanistically, these enlarged organs resulted from an increase in cell proliferation that occurred over a longer developmental time frame relative to wild-type. This organ enlargement was dependent on the receptor-like kinase, ERECTA (ER). This and lateral organ patterning phenotypes in cuc2-1D suggest that miRNA164 and CUC2 are critical regulators of both processes. Therefore, we propose that miRNA164 and CUC2 form a central regulatory module that acts as a governor of lateral organ patterning and expansion.

A microRNA-transcription factor module regulates lateral organ size and patterning in Arabidopsis

Precise regulatory mechanisms are necessary to properly control the enlargement and patterning of plant lateral organs. However, our understanding of the regulatory modules that govern both of these processes is limited. An emerging theme in plant development is microRNA (miRNA)-mediated gene regulation of transcription factors, including several NAC domain family members such as CUP-SHAPED COTYLEDON2 (CUC2). We uncovered a novel allele of CUC2, cuc2-1D, that revealed important functions of miRNAs and CUC2 in a regulatory module governing lateral organ enlargement and patterning. cuc2-1D carried a single point mutation in the CUC2 miRNA target site, disrupting miRNA targeting. Disruption of the tight balance between CUC2 and its targeting miRNA, miRNA164, led to over-accumulation of CUC2 mRNA and expansion of the CUC2 expression domain. cuc2-1D plants had enlarged vegetative and reproductive lateral organs relative to wild-type plants. Mechanistically, these enlarged organs resulted from an increase in cell proliferation that occurred over a longer developmental time frame relative to wild-type. This organ enlargement was dependent on the receptor-like kinase, ERECTA (ER). This and lateral organ patterning phenotypes in cuc2-1D suggest that miRNA164 and CUC2 are critical regulators of both processes. Therefore, we propose that miRNA164 and CUC2 form a central regulatory module that acts as a governor of lateral organ patterning and expansion.