Telomere dynamics and oxidative stress in Arabidopsis grown in lunar regolith simulant.

NASA envisions a future where humans establish a thriving colony on the Moon by 2050. Plants will be essential for this endeavor, but little is known about their adaptation to extraterrestrial bodies. The capacity to grow plants in lunar regolith would represent a major step towards this goal by minimizing the reliance on resources transported from Earth.

Arabidopsis telomerase takes off by uncoupling enzyme activity from telomere length maintenance in space.

Spaceflight-induced changes in astronaut telomeres have garnered significant attention in recent years. While plants represent an essential component of future long-duration space travel, the impacts of spaceflight on plant telomeres and telomerase have not been examined. Here we report on the telomere dynamics of Arabidopsis thaliana grown aboard the International Space Station.

H3.1K27me1 loss confers Arabidopsis resistance to Geminivirus by sequestering DNA repair proteins onto host genome.

The H3 methyltransferases ATXR5 and ATXR6 deposit H3.1K27me1 to heterochromatin to prevent genomic instability and transposon re-activation. Here, we report that atxr5 atxr6 mutants display robust resistance to Geminivirus.

Quantification of 8- in Plant Telomeres.

Chemical modifications in DNA impact gene regulation and chromatin structure. DNA oxidation, for example, alters gene expression, DNA synthesis and cell cycle progression. Modification of telomeric DNA by oxidation is emerging as a marker of genotoxic damage and is associated with reduced genome integrity and changes in telomere length and telomerase activity.

Arabidopsis retains vertebrate-type telomerase accessory proteins via a plant-specific assembly.

The recent discovery of the bona-fide telomerase RNA (TR) from plants reveals conserved and unique secondary structure elements and the opportunity for new insight into the telomerase RNP. Here we examine how two highly conserved proteins previously implicated in Arabidopsis telomere maintenance, AtPOT1a and AtNAP57 (dyskerin), engage plant telomerase. We report that AtPOT1a associates with Arabidopsis telomerase via interaction with TERT.

Change and HOAP for the best.

HOAP is a telomere-binding protein that has a conserved role in , but it also needs to evolve quickly to restrict telomeric retrotransposons.

tRNA ADENOSINE DEAMINASE 3 is required for telomere maintenance in Arabidopsis thaliana.

KEY MESSAGE: tRNA Adenosine Deaminase 3 helps to sustain telomere tracts in a telomerase-independent fashion, likely through regulating cellular metabolism. Telomere length maintenance is influenced by a complex web of chromatin and metabolism-related factors. We previously reported that a lncRNA termed AtTER2 regulates telomerase activity in Arabidopsis thaliana in response to DNA damage.

The conserved structure of plant telomerase RNA provides the missing link for an evolutionary pathway from ciliates to humans.

Telomerase is essential for maintaining telomere integrity. Although telomerase function is widely conserved, the integral telomerase RNA (TR) that provides a template for telomeric DNA synthesis has diverged dramatically. Nevertheless, TR molecules retain 2 highly conserved structural domains critical for catalysis: a template-proximal pseudoknot (PK) structure and a downstream stem-loop structure.

Recent emergence and extinction of the protection of telomeres 1c gene in Arabidopsis thaliana.

Duplicate POT1 genes must rapidly diverge or be inactivated. Protection of telomeres 1 (POT1) encodes a conserved telomere binding protein implicated in both chromosome end protection and telomere length maintenance. Most organisms harbor a single POT1 gene, but in the few lineages where the POT1 family has expanded, the duplicate genes have diversified.

βC1 protein encoded in geminivirus satellite concertedly targets MKK2 and MPK4 to counter host defense.

Plant viruses have evolved multiple strategies to overcome host defense to establish an infection. Here, we identified two components of a host mitogen-activated protein kinase (MAPK) cascade, MKK2 and MPK4, as bona fide targets of the βC1 protein encoded by the betasatellite of tomato yellow leaf curl China virus (TYLCCNV). βC1 interacts with the kinase domain of MKK2 and inhibits its activity.

Genome-Wide Investigation of the Role of MicroRNAs in Desiccation Tolerance in the Resurrection Grass .

Drought causes approximately two-thirds of crop and yield loss worldwide. To sustain future generations, there is a need to develop robust crops with enhanced water use efficiency. Resurrection plants are naturally resilient and tolerate up to 95% water loss with the ability to revive upon watering.

The Trojan Horse of the Plant Kingdom.

The advent of host-induced gene silencing (HIGS) technology for the development of pathogen-resistant cultivars led to the discovery of cross-kingdom RNA interference. In a recent Science paper, Cai et al. (2018) discovered that plant extracellular vesicles act as Trojan horses to deliver small RNAs into fungi to fight infection.

Arabidopsis Serrate Coordinates Histone Methyltransferases ATXR5/6 and RNA Processing Factor RDR6 to Regulate Transposon Expression.

Serrate (SE) is a key component in RNA metabolism. Little is known about whether and how it can regulate epigenetic silencing. Here, we report histone methyltransferases ATXR5 and ATXR6 (ATXR5/6) as novel partners of SE.

SWI2/SNF2 ATPase CHR2 remodels pri-miRNAs via Serrate to impede miRNA production.

Chromatin remodelling factors (CHRs) typically function to alter chromatin structure. CHRs also reside in ribonucleoprotein complexes, but little is known about their RNA-related functions. Here we show that CHR2 (also known as BRM), the ATPase subunit of the large switch/sucrose non-fermentable (SWI/SNF) complex, is a partner of the Microprocessor component Serrate (SE).

Transactivator: A New Face of Arabidopsis AGO1.

Argonaute (AGO) proteins execute RNA-induced transcriptional and post-transcriptional gene silencing. In this issue of Developmental Cell, Liu et al. (2018) uncover a nuclear function for Arabidopsis AGO1 in positively regulating gene expression.

RISC-interacting clearing 3'- 5' exoribonucleases (RICEs) degrade uridylated cleavage fragments to maintain functional RISC in .

RNA-induced silencing complex (RISC) is composed of miRNAs and AGO proteins. AGOs use miRNAs as guides to slice target mRNAs to produce truncated 5' and 3' RNA fragments. The 5' cleaved RNA fragments are marked with uridylation for degradation.

The functions of plant small RNAs in development and in stress responses.

Like metazoans, plants use small regulatory RNAs (sRNAs) to direct gene expression. Several classes of sRNAs, which are distinguished by their origin and biogenesis, exist in plants. Among them, microRNAs (miRNAs) and trans-acting small interfering RNAs (ta-siRNAs) mainly inhibit gene expression at post-transcriptional levels.

Geminivirus-encoded TrAP suppressor inhibits the histone methyltransferase SUVH4/KYP to counter host defense.

Transcriptional gene silencing (TGS) can serve as an innate immunity against invading DNA viruses throughout Eukaryotes. Geminivirus code for TrAP protein to suppress the TGS pathway. Here, we identified an Arabidopsis H3K9me2 histone methyltransferase, Su(var)3-9 homolog 4/Kryptonite (SUVH4/KYP), as a bona fide cellular target of TrAP.

Reconstitution Assay of miRNA Biogenesis by Arabidopsis DCL1.

microRNAs (miRNAs) are small non-coding RNAs, regulating most if not all, biological processes in eukaryotic organisms. miRNAs are initially processed from primary transcripts (pri-miRNAs) to produce miRNA precursors (pre-miRNAs), that are further processed into miRNA and its complementary strands (miRNA/*). In Arabidopsis, and possibly other plants, the processing from pri-miRNAs to pre-miRNAs and from pre-miRNAs to miRNA/* are both implemented through Dicer-like 1 (DCL1) complexes.

Bidirectional processing of pri-miRNAs with branched terminal loops by Arabidopsis Dicer-like1.

MicroRNAs (miRNAs) originate from primary transcripts (pri-miRNAs) with characteristic stem-loop structures, and their accurate processing is required for the production of functional miRNAs. Here, using the pri-miR-166 family in Arabidopsis thaliana as a paradigm, we report the crucial role of pri-miRNA terminal loops in miRNA biogenesis. We found that multibranched terminal loops in pri-miR-166s substantially suppress miR-166 expression in vivo.