An integrated reagent toolkit and streamlined protocols work across diverse plant species to enable sophisticated genome edits.

Summary: Processing of double‐stranded RNA precursors into small RNAs is an essential regulator of gene expression in plant development and stress response. Small RNA processing requires the combined activity of a functionally diverse group of molecular components. However, in most of the plant species, there are insufficient mutant resources to functionally characterize each encoding gene. Here, mutations in loci encoding protein machinery involved in small RNA processing in soya bean and Medicago truncatula were generated using the CRISPR/Cas9 and TAL‐effector nuclease (TALEN) mutagenesis platforms. An efficient CRISPR/Cas9 reagent was used to create a bi‐allelic double mutant for the two soya bean paralogous Double‐stranded RNA‐binding2 (GmDrb2a and GmDrb2b) genes. These mutations, along with a CRISPR/Cas9‐generated mutation of the M. truncatula Hua enhancer1 (MtHen1) gene, were determined to be germ‐line transmissible. Furthermore, TALENs were used to generate a mutation within the soya bean Dicer‐like2 gene. CRISPR/Cas9 mutagenesis of the soya bean Dicer‐like3 gene and the GmHen1a gene was observed in the T₀ generation, but these mutations failed to transmit to the T₁ generation. The irregular transmission of induced mutations and the corresponding transgenes was investigated by whole‐genome sequencing to reveal a spectrum of non‐germ‐line‐targeted mutations and multiple transgene insertion events. Finally, a suite of combinatorial mutant plants were generated by combining the previously reported Gmdcl1a, Gmdcl1b and Gmdcl4b mutants with the Gmdrb2ab double mutant. Altogether, this study demonstrates the synergistic use of different genome engineering platforms to generate a collection of useful mutant plant lines for future study of small RNA processing in legume crops.

Genome-wide association (GWA) studies offer the opportunity to identify genes that contribute to naturally occurring variation in quantitative traits. However, GWA relies exclusively on statistical association, so functional validation is necessary to make strong claims about gene function. We used a combination of gene-disruption platforms (Tnt1 retrotransposons, hairpin RNA-interference constructs, and CRISPR/Cas9 nucleases) together with randomized, well-replicated experiments to evaluate the function of genes that an earlier GWA study in Medicago truncatula had identified as candidates contributing to variation in the symbiosis between legumes and rhizobia. We evaluated ten candidate genes found in six clusters of strongly associated single nucleotide polymorphisms, selected on the basis of their strength of statistical association, proximity to annotated gene models, and root or nodule expression. We found statistically significant effects on nodule production for three candidate genes, each validated in two independent mutants. Annotated functions of these three genes suggest their contributions to quantitative variation in nodule production occur through processes not previously connected to nodulation, including phosphorous supply and salicylic acid-related defense response. These results demonstrate the utility of GWA combined with reverse mutagenesis technologies to discover and validate genes contributing to naturally occurring variation in quantitative traits. The results highlight the potential for GWA to complement forward genetics in identifying the genetic basis of ecologically and economically important traits.

Potato (Solanum tuberosum L.) is the third most important crop worldwide and a staple food for many people worldwide. Genetically, it poses many challenges for traditional breeding due to its autotetraploid nature and its tendency toward inbreeding depression. Breeding programs have focused on productivity, nutritional quality, and disease resistance. Some of these traits exist in wild potato relatives but their introgression into elite cultivars can take many years and, for traits such as pest resistance, their effect is often short-lasting. These problems can be addressed by genetic modification (GM) or gene editing (GE) and open a wide horizon for potato crop improvement. Current genetically modified and gene edited varieties include those with Colorado potato beetle and late blight resistance, reduction in acrylamide, and modified starch content. RNAi hairpin technology can be used to silence the haplo-alleles of multiple genes simultaneously, whereas optimization of newer gene editing technologies such as base and prime editing will facilitate the routine generation of advanced edits across the genome. These technologies will likely gain further relevance as increased target specificity and decreased off-target effects are demonstrated. In this Review, we discuss recent work related to these technologies in potato improvement.

Growing knowledge about crop domestication, combined with increasingly powerful gene-editing toolkits, sets the stage for the continual domestication of crop wild relatives and other lesser-known plant species.

Small non-protein-coding microRNAs (miRNAs) are present in most eukaryotes and are central effectors of RNA silencing mediated mechanisms for gene expression regulation. In plants, DICER-LIKE1 (DCL1) is the founding member of a highly conserved family of RNase III-like endonucleases that function as core machinery proteins to process hairpin-like precursor transcripts into mature miRNAs, small regulatory RNAs, 21 to 22 nucleotides in length. Zinc-finger nucleases (ZFNs) were used to generate single and double-mutants of putative soybean DCL1 homologs, DCL1a and DCL1b, to confirm their functional role(s) in the soybean miRNA pathway. Neither DCL1 single mutant, dcl1a or dcl1b plants, exhibited a pronounced morphological or molecular phenotype. The dcl1a/dcl1b double mutant however, expressed a strong morphological phenotype, characterized by reduced seed size and aborted seedling development, in addition to defective miRNA precursor transcript processing efficiency and deregulated miRNA target gene expression. Together, these findings indicate that the two soybean DCL1 paralogs, DCL1a and DCL1b, largely play functionally redundant roles in the miRNA pathway and are essential for normal plant development.