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1. Evidence of a novel silencing effect on transgenes in the Arabidopsis thaliana sperm cell

   https://doi.org/10.1093/plcell/koad219  

   Ohnishi, Yukinosuke; Kawashima, Tomokazu (August 2023, The Plant Cell)

   Abstract We encountered unexpected transgene silencing in Arabidopsis thaliana sperm cells; transgenes encoding proteins with no specific intracellular localization (cytoplasmic proteins) were silenced transcriptionally or posttranscriptionally. The mRNA of cytoplasmic protein transgenes tagged with a fluorescent protein gene was significantly reduced, resulting in undetectable fluorescent protein signals in the sperm cell. Silencing of the cytoplasmic protein transgenes in the sperm cell did not affect the expression of either its endogenous homologous genes or cotransformed transgenes encoding a protein with targeted intracellular localization. This transgene silencing in the sperm cell persisted in mutants of the major gene silencing machinery including DNA methylation. The incomprehensible, yet real, transgene silencing phenotypes occurring in the sperm cell could mislead the interpretation of experimental results in plant reproduction, and this Commentary calls attention to that risk and highlights details of this novel cytoplasmic protein transgene silencing. 

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2. Exploiting somatic piRNAs in Bemisia tabac i enables novel gene silencing through RNA feeding

   https://doi.org/10.26508/lsa.202000731  

   Mondal, Mosharrof; Brown, Judith K; Flynt, Alex (August 2020, Life Science Alliance)

   null (Ed.)

   RNAi promises to reshape pest control by being nontoxic, biodegradable, and species specific. However, due to the plastic nature of RNAi, there is a significant variability in responses. In this study, we investigate small RNA pathways and processing of ingested RNAi trigger molecules in a hemipteran plant pest, the whitefly Bemisia tabaci . Unlike Drosophila , where the paradigm for insect RNAi technology was established, whitefly has abundant somatic piwi-associated RNAs (piRNAs). Long regarded as germline restricted, piRNAs are common in the soma of many invertebrates. We sought to exploit this for a novel gene silencing approach. The main principle of piRNA biogenesis is the recruitment of target RNA fragments into the pathway. As such, we designed synthetic RNAs to possess complementarity to the loci we annotated. Following feeding of these exogenous piRNA triggers knockdown as effective as conventional siRNA-only approaches was observed. These results demonstrate a new approach for RNAi technology that could be applicable to dsRNA-recalcitrant pest species and could be fundamental to realizing insecticidal RNAi against pests. 

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3. The epigenetic factor FVE orchestrates cytoplasmic SGS3-DRB4-DCL4 activities to promote transgene silencing in Arabidopsis

   https://doi.org/10.1126/sciadv.abf3898  

   Sun, Di; Li, Yanjun; Ma, Zeyang; Yan, Xingxing; Li, Niankui; Shang, Baoshuan; Hu, Xiaomei; Cui, Kai; Koiwa, Hisashi; Zhang, Xiuren (August 2021, Science Advances)

   null (Ed.)
4. Silencing the genome with linker histones

   https://doi.org/10.1073/pnas.2009513117  

   Hansen, Jeffrey C. (June 2020, Proceedings of the National Academy of Sciences)
5. Structural analysis of Phytophthora suppressor of RNA silencing 2 (PSR2) reveals a conserved modular fold contributing to virulence

   https://doi.org/10.1073/pnas.1819481116  

   He, Jinqiu; Ye, Wenwu; Choi, Du Seok; Wu, Baixing; Zhai, Yi; Guo, Baodian; Duan, Shuyi; Wang, Yuanchao; Gan, Jianhua; Ma, Wenbo; et al (April 2019, Proceedings of the National Academy of Sciences)

   Phytophthora are eukaryotic pathogens that cause enormous losses in agriculture and forestry. Each Phytophthora species encodes hundreds of effector proteins that collectively have essential roles in manipulating host cellular processes and facilitating disease development. Here we report the crystal structure of the effector Phytophthora suppressor of RNA silencing 2 (PSR2). PSR2 produced by the soybean pathogen Phytophthora sojae ( Ps PSR2) consists of seven tandem repeat units, including one W-Y motif and six L-W-Y motifs. Each L-W-Y motif forms a highly conserved fold consisting of five α-helices. Adjacent units are connected through stable, directional linkages between an internal loop at the C terminus of one unit and a hydrophobic pocket at the N terminus of the following unit. This unique concatenation results in an overall stick-like structure of Ps PSR2. Genome-wide analyses reveal 293 effectors from five Phytophthora species that have the Ps PSR2-like arrangement, that is, containing a W-Y motif as the “start” unit, various numbers of L-W-Y motifs as the “middle” units, and a degenerate L-W-Y as the “end” unit. Residues involved in the interunit interactions show significant conservation, suggesting that these effectors also use the conserved concatenation mechanism. Furthermore, functional analysis demonstrates differential contributions of individual units to the virulence activity of Ps PSR2. These findings suggest that the L-W-Y fold is a basic structural and functional module that may serve as a “building block” to accelerate effector evolution in Phytophthora . 

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