Identification and characterization of the key enzyme in the biosynthesis of the neurotoxin β-ODAP in grass pea

Evaluation of genetic diversity and elucidation of population structure of Lathyrus accessions using agro-morphological characters and ISSR technique

Genetic diversity and population structure were evaluated for 36 Lathyrus L. accessions using agronomic characters and ISSR markers. The agronomic characters and ISSR markers showed a wide genetic diversity between Lathyrus accessions. The significant association between 1000 seed weight and total seed protein percentage in Lathyrus accessions revealed that both characters were under independent genetic control. The total number of alleles generated by the markers was 336, revealing 100% polymorphism. The polymorphic information content (PIC), effective multiplex ratio (EMR), marker index (MI), and resolving power (RP) of the markers were 0.75, 16.46, 17.83, and 2.70, respectively, confirming the great variation in Lathyrus accessions. The AMOVA test indicated that 93% of all genetic variation was found within accessions and 7% between accessions. The Ewens-Watterson test for neutrality indicated that the nine markers were neutral, and most of the genetic diversity resided in accessions, with the exception of Lathyrus aphaca from Bulgaria, confirming AMOVA results. The genetic diversity (h) and Shannon's information index were 0.34 and 0.52, respectively, revealing that maker OPA01-812 was highly recommended for distinguishing Lathyrus accessions. The genetic differentiation among accessions (GST) was 0.03, whereas the number of migrants per generation based on Wright's equation (Nmw) was 18.12. However, the probability (P) of the chi-square values exceeded 0.05 for the nine markers, indicating the low heterogeneity between the investigated accessions. Cluster and correspondence analyses for ISSR results showed that the genetic diversity among Lathyrus accessions was not influenced by their geographical origin. They also revealed that Lathyrus sativus and Lathyrus cicera were not derived from the same ancestor. In conclusion, we recommended (1) Lathyrus sativus PI 179299 for breeding for new cultivars with a high yield and low β-ODAP percentage and (2) ISSR markers for characterizing and differentiating between Lathyrus accessions.

Genome editing of an oxalyl-CoA synthetase gene in Lathyrus sativus reveals its role in oxalate metabolism

KEY MESSAGE

Established an Agrobacterium-mediated hairy root transformation system for gene function analysis in Lathyrus sativus. Arabidopsis mutant complementation and genome editing in Lathyrus confirmed role of LsOCS in the oxalate metabolism. Grass pea (Lathyrus sativus) is a resilient legume cultivated for its protein-rich seeds and fodder. However, the presence of a naturally occurring neurotoxin, β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), which causes neurolathyrism, limits its extensive cultivation. This paper reports the in-planta characterization of oxalyl-CoA synthetase (OCS), an enzyme involved in oxalate metabolism and important in the oxalylating step leading to β-ODAP production in Lathyrus. For this, we used complementation experiments in an Arabidopsis OCS mutant. The LsOCS-complemented lines showed oxalate content similar to wild-type levels, and the analysis of seeds by field emission scanning electron microscope (FESEM) showed that the LsOCS-complemented lines were rescued from seed-coat defects found in the mutant seeds. We used genome editing of LsOCS in Lathyrus hairy roots to further characterize LsOCS function. The mutations in LsOCS resulted in the accumulation of oxalate in the hairy roots of Lathyrus, as observed in Arabidopsis mutants, but did not affect the ODAP levels. The hairy root genome editing system could serve as a rapid tool for functional studies of Lathyrus genes and optimizing the agronomic traits.

The Potential of CRISPR/Cas9 to Circumvent the Risk Factor Neurotoxin β-N-oxalyl-L-α, β-diaminopropionic acid Limiting Wide Acceptance of the Underutilized Grass Pea (Lathyrus sativus L.)

Grass pea (Lathyrus sativus L.) is a protein-rich crop that is resilient to various abiotic stresses, including drought. However, it is not cultivated widely for human consumption due to the neurotoxin β-N-oxalyl-L-α, β-diaminopropionic acid (β-ODAP) and its association with neurolathyrism. Though some varieties with low β-ODAP have been developed through classical breeding, the β-ODAP content is increasing due to genotype x environment interactions. This review covers grass pea nutritional quality, β-ODAP biosynthesis, mechanism of paralysis, traditional ways to reduce β-ODAP, candidate genes for boosting sulfur-containing amino acids, and the potential and targets of gene editing to reduce β-ODAP content. Recently, two key enzymes (β-ODAP synthase and β-cyanoalanine synthase) have been identified in the biosynthetic pathway of β-ODAP. We proposed four strategies through which the genes encoding these enzymes can be targeted and suppressed using CRISPR/Cas9 gene editing. Compared to its homology in Medicago truncatula, the grass pea β-ODAP synthase gene sequence and β-cyanoalanine synthase showed 62.9% and 95% similarity, respectively. The β-ODAP synthase converts the final intermediate L-DAPA into toxic β-ODAP, whist β-cyanoalanine synthase converts O-Acetylserine into β-isoxazolin-5-on-2-yl-alanine. Since grass pea is low in methionine and cysteine amino acids, improvement of these amino acids is also needed to boost its protein content. This review contains useful resources for grass pea improvement while also offering potential gene editing strategies to lower β-ODAP levels.

Remodeling metabolism of Corynebacterium glutamicum for high-level dencichine production

Dencichine, a sought-after compound in the medical industry, requires a more efficient and sustainable production method than the current plant extraction process. This study successfully remodeled the metabolic pathway of Corynebacterium glutamicum to produce dencichine from the precursors of L-2,3-diaminopropionate (L-DAP) and oxalyl-coenzyme A. Firstly, a synthetic pathway for L-DAP was established by introducing exogenous enzymes ZmaU/ZmaV. This resulted in a production of 628 mg/L by overexpressing key genes and reducing the endogenous competitive pathway. Secondly, an oxalyl-CoA synthetic pathway was created through the enzymatic conversion of glyoxylate by introducing heterologous enzymes. Finally, with the integration of the exogenous enzyme BAHD, de novo synthesis of dencichine in C. glutamicum was achieved, and production reached 31.75 mg/L within 48-hour fermentation. This achievement represents the first successful biosynthesis of dencichine in C. glutamicum, offering a promising approach for natural product through microbial fermentation.

Exploiting genetic and genomic resources to enhance productivity and abiotic stress adaptation of underutilized pulses

Underutilized pulses and their wild relatives are typically stress tolerant and their seeds are packed with protein, fibers, minerals, vitamins, and phytochemicals. The consumption of such nutritionally dense legumes together with cereal-based food may promote global food and nutritional security. However, such species are deficient in a few or several desirable domestication traits thereby reducing their agronomic value, requiring further genetic enhancement for developing productive, nutritionally dense, and climate resilient cultivars. This review article considers 13 underutilized pulses and focuses on their germplasm holdings, diversity, crop-wild-crop gene flow, genome sequencing, syntenic relationships, the potential for breeding and transgenic manipulation, and the genetics of agronomic and stress tolerance traits. Recent progress has shown the potential for crop improvement and food security, for example, the genetic basis of stem determinacy and fragrance in moth bean and rice bean, multiple abiotic stress tolerant traits in horse gram and tepary bean, bruchid resistance in lima bean, low neurotoxin in grass pea, and photoperiod induced flowering and anthocyanin accumulation in adzuki bean have been investigated. Advances in introgression breeding to develop elite genetic stocks of grass pea with low β-ODAP (neurotoxin compound), resistance to Mungbean yellow mosaic India virus in black gram using rice bean, and abiotic stress adaptation in common bean, using genes from tepary bean have been carried out. This highlights their potential in wider breeding programs to introduce such traits in locally adapted cultivars. The potential of de-domestication or feralization in the evolution of new variants in these crops are also highlighted.

Critical Sites of Serine Acetyltransferase in Lathyrus sativus L. Affecting Its Enzymatic Activities

LsSAT2 (serine acetyltransferase in Lathyrus sativus) is the rate-limiting enzyme in biosynthesis of β-N-oxalyl-l-α,β-diaminopropionic acid (β-ODAP), a neuroactive metabolite distributed widely in several plant species including Panax notoginseng, Panax ginseng, and L. sativus. The enzymatic activity of LsSAT2 is post-translationally regulated by its involvement in the cysteine regulatory complex in mitochondria via interaction with β-CAS (β-cyanoalanine synthase). In this study, the binding sites of LsSAT2 with the substrate Ser were first determined as Glu²⁹⁰, Arg³¹⁶, and His³¹⁷ and the catalytic sites were determined as Asp²⁶⁷, Asp²⁸¹, and His²⁸² via site-directed/truncated mutagenesis, in vitro enzymatic activity assay, and functional complementation of the SAT-deficient Escherichia coli strain JM39. Furthermore, the C-terminal 10-residue peptide of LsSAT2 is confirmed to be critical to interact with LsCAS, and Ile³³⁶ in C10 peptide is the critical amino acid. These results will enhance our understanding of the regulation of LsSAT2 activities and the biosynthesis of β-ODAP in L. sativus.

Asymmetric horseshoe-like assembly of peroxisomal yeast oxalyl-CoA synthetase

Oxalyl-CoA synthetase from Saccharomyces cerevisiae is one of the most abundant peroxisomal proteins in yeast and hence has become a model to study peroxisomal translocation. It contains a C-terminal Peroxisome Targeting Signal 1, which however is partly dispensable, suggesting additional receptor bindings sites. To unravel any additional features that may contribute to its capacity to be recognized as peroxisomal target, we determined its assembly and overall architecture by an integrated structural biology approach, including X-ray crystallography, single particle cryo-electron microscopy and small angle X-ray scattering. Surprisingly, it assembles into mixture of concentration-dependent dimers, tetramers and hexamers by dimer self-association. Hexameric particles form an unprecedented asymmetric horseshoe-like arrangement, which considerably differs from symmetric hexameric assembly found in many other protein structures. A single mutation within the self-association interface is sufficient to abolish any higher-level oligomerization, resulting in a homogenous dimeric assembly. The small C-terminal domain of yeast Oxalyl-CoA synthetase is connected by a partly flexible hinge with the large N-terminal domain, which provides the sole basis for oligomeric assembly. Our data provide a basis to mechanistically study peroxisomal translocation of this target.

Genomics and biochemical analyses reveal a metabolon key to β-L-ODAP biosynthesis in Lathyrus sativus

Grass pea (Lathyrus sativus L.) is a rich source of protein cultivated as an insurance crop in Ethiopia, Eritrea, India, Bangladesh, and Nepal. Its resilience to both drought and flooding makes it a promising crop for ensuring food security in a changing climate. The lack of genetic resources and the crop's association with the disease neurolathyrism have limited the cultivation of grass pea. Here, we present an annotated, long read-based assembly of the 6.5 Gbp L. sativus genome. Using this genome sequence, we have elucidated the biosynthetic pathway leading to the formation of the neurotoxin, β-L-oxalyl-2,3-diaminopropionic acid (β-L-ODAP). The final reaction of the pathway depends on an interaction between L. sativus acyl-activating enzyme 3 (LsAAE3) and a BAHD-acyltransferase (LsBOS) that form a metabolon activated by CoA to produce β-L-ODAP. This provides valuable insight into the best approaches for developing varieties which produce substantially less toxin.

Biotechnological detoxification: an unchanging source-sink balance strategy for crop improvement

The wide occurrence of natural phytotoxins renders many crops unfit for human consumption. To overcome this problem and produce detoxified crop varieties, we propose the use of biotechnological strategies that can enhance the harvest index without the need to increase crop biomass or alter whole plant architecture.