In-locus gene silencing in plants using genome editing.

Gene silencing is crucial in crop breeding for desired trait development. RNA interference (RNAi) has been used widely but is limited by ectopic expression of transgenes and genetic instability. Introducing an upstream start codon (uATG) into the 5'untranslated region (5'UTR) of a target gene may 'silence' the target gene by inhibiting protein translation from the primary start codon (pATG). Here, we report an efficient gene silencing method by introducing a tailor-designed uATG-containing element (ATGE) into the 5'UTR of genes in plants, occupying the original start site to act as a new pATG. Using base editing to introduce new uATGs failed to silence two of the tested three rice genes, indicating complex regulatory mechanisms. Precisely inserting an ATGE adjacent to pATG achieved significant target protein downregulation. Through extensive optimization, we demonstrated this strategy substantially and consistently downregulated target protein expression. By designing a bidirectional multifunctional ATGE4, we enabled tunable knockdown from 19% to 89% and observed expected phenotypes. Introducing ATGE into Waxy, which regulates starch synthesis, generated grains with lower amylose, revealing the value for crop breeding. Together, we have developed a programmable and robust method to knock down gene expression in plants, with potential for biological mechanism exploration and crop enhancement.

Targeted G-to-T base editing for generation of novel herbicide-resistance gene alleles in rice.

A newly developed rice guanine base editor (OsGTBE) achieves targeted and efficient G-to-T editing (C-to-A in the opposite strand) in rice. Using OsGTBE to edit endogenous herbicide-resistant loci generated several novel alleles conferring herbicide resistance, highlighting its utility in creating valuable germplasm and enhancing genetic diversity..

Efficient and multiplex gene upregulation in plants through CRISPR/Cas-mediated knock-in of enhancers.

Gene upregulation through genome editing is important for plant research and breeding. Targeted insertion of short transcriptional enhancers (STEs) into gene promoters may offer a universal solution akin to transgene-mediated overexpression, while avoiding the drawbacks associated with transgenesis. Here, we introduce an "in-locus activation" technique in rice that leverages specifically screened STEs for refined, heritable, and multiplexed gene upregulation. To address the scarcity of potent enhancers, we developed a large-scale mining approach and discovered a suite of STEs capable of enhancing gene expression in rice protoplasts. The in-locus integration of these STEs into eight rice genes resulted in substantial transcriptional enhancements, with up to 869.1-fold increases in the edited plants. Employing a variety of STEs, we achieved delicate control of gene expression, enabling the fine-tuning of key phenotypic traits such as plant height. Our approach also enabled efficient multiplexed gene upregulation, with up to four genes simultaneously activated, significantly enhancing the nicotinamide mononucleotide (NMN) metabolic pathway. Importantly, heritability studies from the T0 to T3 generations confirmed the stable and heritable nature of STE-driven gene activation. Coupled with our STE-mining technique, in-locus activation holds great promise to make gene upregulation a major application of genome editing in plant research and breeding.

Efficient and heritable A-to-K base editing in rice and tomato.

Cytosine and adenosine base editors (CBE and ABE) have been widely used in plants, greatly accelerating gene function research and crop breeding. Current base editors can achieve efficient A-to-G and C-to-T/G/A editing. However, efficient and heritable A-to-Y (A-to-T/C) editing remains to be developed in plants. In this study, a series of A-to-K base editor (AKBE) systems were constructed for monocot and dicot plants. Furthermore, nSpCas9 was replaced with the PAM-less Cas9 variant (nSpRY) to expand the target range of the AKBEs. Analysis of 228 T0 rice plants and 121 T0 tomato plants edited using AKBEs at 18 endogenous loci revealed that, in addition to highly efficient A-to-G substitution (41.0% on average), the plant AKBEs can achieve A-to-T conversion with efficiencies of up to 25.9 and 10.5% in rice and tomato, respectively. Moreover, the rice-optimized AKBE generates A-to-C conversion in rice, with an average efficiency of 1.8%, revealing the significant value of plant-optimized AKBE in creating genetic diversity. Although most of the A-to-T and A-to-C edits were chimeric, desired editing types could be transmitted to the T1 offspring, similar to the edits generated by the traditional ABE8e. Besides, using AKBEs to target tyrosine (Y, TAT) or cysteine (C, TGT) achieved the introduction of an early stop codon (TAG/TAA/TGA) of target genes, demonstrating its potential use in gene disruption.

Rapid and dynamic detection of endogenous proteins through in-locus tagging in rice.

Understanding the behavior of endogenous proteins is crucial for functional genomics, yet their dynamic characterization in plants presents substantial challenges. While mammalian studies have leveraged in-locus tagging with the luminescent HiBiT peptide and genome editing for rapid quantification of native proteins, this approach remained unexplored in plants. Here, we introduce the in-locus HiBiT tagging of rice proteins and demonstrate its feasibility in plants. We found that although traditional HiBiT blotting works in rice, it failed to detect two of the three tagged proteins, which is attributed to the low luminescence activity in plants. To overcome this limitation, we engaged in extensive optimization, culminating in a new luciferin substrate coupled with a refined reaction protocol that enhanced luminescence by up to 6.9-fold. This innovation led to the development of TagBIT (tagging with HiBiT), a robust method for high-sensitivity protein characterization in plants. Our application of TagBIT to seven rice genes illustrates its versatility on endogenous proteins, enabling antibody-free protein blotting, real-time protein quantification via luminescence, in-situ visualization using a cross-breeding strategy, and effective immunoprecipitation for protein interaction analysis. The heritable nature of this system, confirmed across T1 to T3 generations, positions TagBIT as a powerful tool for protein study in plant biology.