Single Molecule Imaging of T-DNA Intermediates Following Agrobacterium tumefaciens Infection in Nicotiana benthamiana

Genomic consequences associated with Agrobacterium-mediated transformation of plants

Attenuated strains of the naturally occurring plant pathogen Agrobacterium tumefaciens can transfer virtually any DNA sequence of interest to model plants and crops. This has made Agrobacterium-mediated transformation (AMT) one of the most commonly used tools in agricultural biotechnology. Understanding AMT, and its functional consequences, is of fundamental importance given that it sits at the intersection of many fundamental fields of study, including plant-microbe interactions, DNA repair/genome stability, and epigenetic regulation of gene expression. Despite extensive research and use of AMT over the last 40 years, the extent of genomic disruption associated with integrating exogenous DNA into plant genomes using this method remains underappreciated. However, new technologies like long-read sequencing make this disruption more apparent, complementing previous findings from multiple research groups that have tackled this question in the past. In this review, we cover progress on the molecular mechanisms involved in Agrobacterium-mediated DNA integration into plant genomes. We also discuss localized mutations at the site of insertion and describe the structure of these DNA insertions, which can range from single copy insertions to large concatemers, consisting of complex DNA originating from different sources. Finally, we discuss the prevalence of large-scale genomic rearrangements associated with the integration of DNA during AMT with examples. Understanding the intended and unintended effects of AMT on genome stability is critical to all plant researchers who use this methodology to generate new genetic variants.

Inhibition of mTOR decreases insoluble proteins burden by reducing translation in C. elegans

Aging animals accumulate insoluble proteins as a consequence of a decline of proteostatic maintenance with age. In Caenorhabditis elegans, for instance, levels of detergent-insoluble proteins increase with age. In longer-lived strains of C. elegans, this accumulation occurs more slowly, implying a link to lifespan determination. We further explored this link and found that detergent-insoluble proteins accumulate more rapidly at higher temperatures, a condition where lifespan is short. We employed a C. elegans strain carrying a GFP transcriptional reporter under the control of a heat shock (hsp-16.2) promoter to investigate the dynamics of proteostatic failure in individual nematodes. We found that early, sporadic activation of hsp-16.2 was predictive of shorter remaining lifespan in individual nematodes. Exposure to rapamycin, resulting in reduced mTOR signaling, delayed spurious expression, extended lifespan, and delayed accumulation of insoluble proteins, suggesting that targets downstream of the mTOR pathway regulate the accumulation of insoluble proteins. We specifically explored ribosomal S6 kinase (rsks-1) as one such candidate and found that RNAi against rsks-1 also resulted in less age-dependent accumulation of insoluble proteins and extended lifespan. Our results demonstrate that inhibition of protein translation via reduced mTOR signaling resulted in slower accumulation of insoluble proteins, delayed proteostatic crisis, and extended lifespan in C. elegans.