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1. Strategies of desiccation tolerance vary across life phases in the moss Syntrichia caninervis

   https://doi.org/10.1002/ajb2.1571  

   Coe, Kirsten K. ; Greenwood, Joshua L. ; Slate, Mandy L. ; Clark, Theresa A. ; Brinda, John C. ; Fisher, Kirsten M. ; Mishler, Brent D. ; Bowker, Matthew A. ; Oliver, Melvin J. ; Ebrahimi, Sotodeh ; et al ( November 2020 , American Journal of Botany)

   Desiccation tolerance (DT) is a widespread phenomenon among land plants, and variable ecological strategies for DT are likely to exist. UsingSyntrichia caninervis, a dryland moss and model system used in DT studies, we hypothesized that DT is lowest in juvenile (protonemal) tissues, highest in asexual reproductive propagules (gemmae), and intermediate in adults (shoots). We tested the long‐standing hypothesis of an inherent constitutive strategy of DT in this species.

   Plants were rapidly dried to levels of equilibrating relative humidity (RHeq) ranging from 0 to 93%. Postrehydration recovery was assessed using chlorophyll fluorescence, regeneration rates, and visual tissue damage. For each life phase, we estimated the minimum rate of drying (RoD_min) atRHeq= 42% that did not elicit damage 24 h postrehydration.

   DT strategy varied with life phase, with adult shoots having the lowestRoD_min(10‒25 min), followed by gemmae (3‒10 h) and protonema (14‒20 h). Adult shoots exhibited no detectable damage 24 h postrehydration following a rapid‐dry only at the highestRHeqused (93%), but when dried to lower RHs the response declined to <50% of control fluorescence values. Notably, immediately following rehydration (0 h postrehydration), shoots were damaged below control levels of fluorescence regardless of theRHeq, thus implicating damage.

   Life phases of the mossS. caninervishad a range of strategies from near constitutive (adult shoots) to demonstrably inducible (protonema). A new response variable for assessing degree of DT is introduced as the minimum rate of drying from which full recovery occurs.

    

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2. Desiccation induces varied responses within a soil bacterial genus

   https://doi.org/10.1111/1462-2920.16494  

   Scales, N. C. ; Huynh, K. T. ; Weihe, C. ; Martiny, J. B. H. ( September 2023 , Environmental Microbiology)

   Desiccation impacts a suite of physiological processes in microbes by elevating levels of damaging reactive oxygen species and inducing DNA strand breaks. In response to desiccation‐induced stress, microbes have evolved specialized mechanisms to help them survive. Here, we performed a 128‐day lab desiccation experiment on nine strains from three clades of an abundant soil bacterium,Curtobacterium. We sequenced RNA from each strain at three time points to investigate their response.Curtobacteriumwas highly resistant to desiccation, outlasting bothEscherichia coliand a famously DNA damage‐resistant bacterium,Deinococcus radiodurans. However, within the genus, there were also 10‐fold differences in survival rates among strains. Transcriptomic profiling revealed responses shared within the genus including up‐regulation of genes involved in DNA damage repair, osmolyte production, and efflux pumps, but also up‐regulation of pathways and genes unique to the three clades. For example, trehalose synthesis geneotsB, the chaperonegroEL, and the oxygen scavengerkatAwere all found in either one or two clades but not the third. Here, we provide evidence of considerable variation in closely related strains, and further elucidation of the phylogenetic conservation of desiccation tolerance remains an important goal for microbial ecologists.

    

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3. To dry perchance to live: Insights from the genome of the desiccation‐tolerant biocrust moss Syntrichia caninervis

   https://doi.org/10.1111/tpj.15116  

   Silva, Anderson T. ; Gao, Bei ; Fisher, Kirsten M. ; Mishler, Brent D. ; Ekwealor, Jenna T. B. ; Stark, Lloyd R. ; Li, Xiaoshuang ; Zhang, Daoyuan ; Bowker, Matthew A. ; Brinda, John C. ; et al ( December 2020 , The Plant Journal)

   With global climate change, water scarcity threatens whole agro/ecosystems. The desert mossSyntrichia caninervis, an extremophile, offers novel insights into surviving desiccation and heat. The sequencedS. caninervisgenome consists of 13 chromosomes containing 16 545 protein‐coding genes and 2666 unplaced scaffolds. Syntenic relationships within theS.caninervisandPhyscomitrellapatensgenomes indicate theS. caninervisgenome has undergone a single whole genome duplication event (compared to two forP. patens) and evidence suggests chromosomal or segmental losses in the evolutionary history ofS. caninervis. The genome contains a large sex chromosome composed primarily of repetitive sequences with a large number ofCopiaandGypsyelements. Orthogroup analyses revealed an expansion ofELIPgenes encoding proteins important in photoprotection. The transcriptomic response to desiccation identified four structural clusters of novel genes. The genomic resources established for this extremophile offer new perspectives for understanding the evolution of desiccation tolerance in plants.

    

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4. Syntrichia ruralis : emerging model moss genome reveals a conserved and previously unknown regulator of desiccation in flowering plants

   https://doi.org/10.1111/nph.19620  

   Zhang, Xiaodan ; Ekwealor, Jenna T. B. ; Mishler, Brent D. ; Silva, Anderson T. ; Yu, Li'ang ; Jones, Andrea K. ; Nelson, Andrew D. L. ; Oliver, Melvin J. ( February 2024 , New Phytologist)

   Water scarcity, resulting from climate change, poses a significant threat to ecosystems.Syntrichia ruralis, a dryland desiccation‐tolerant moss, provides valuable insights into survival of water‐limited conditions.

   We sequenced the genome ofS. ruralis, conducted transcriptomic analyses, and performed comparative genomic and transcriptomic analyses with existing genomes and transcriptomes, including with the close relativeS. caninervis. We took a genetic approach to characterize the role of anS. ruralistranscription factor, identified in transcriptomic analyses, inArabidopsis thaliana.

   The genome was assembled into 12 chromosomes encompassing 21 169 protein‐coding genes. Comparative analysis revealed copy number and transcript abundance differences in known desiccation‐associated gene families, and highlighted genome‐level variation among species that may reflect adaptation to different habitats. A significant number of abscisic acid (ABA)‐responsive genes were found to be negatively regulated by a MYB transcription factor (MYB55) that was upstream of theS. ruralisortholog of ABA‐insensitive 3 (ABI3). We determined that this conserved MYB transcription factor, uncharacterized inArabidopsis, acts as a negative regulator of an ABA‐dependent stress response inArabidopsis.

   The new genomic resources from this emerging model moss offer novel insights into how plants regulate their responses to water deprivation.

    

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5. A comparative genomics examination of desiccation tolerance and sensitivity in two sister grass species

   https://doi.org/10.1073/pnas.2118886119  

   Chávez Montes, Ricardo A. ; Haber, Anna ; Pardo, Jeremy ; Powell, Robyn F. ; Divisetty, Upendra K. ; Silva, Anderson T. ; Hernández-Hernández, Tania ; Silveira, Vanildo ; Tang, Haibao ; Lyons, Eric ; et al ( February 2022 , Proceedings of the National Academy of Sciences)

   Desiccation tolerance is an ancient and complex trait that spans all major lineages of life on earth. Although important in the evolution of land plants, the mechanisms that underlay this complex trait are poorly understood, especially for vegetative desiccation tolerance (VDT). The lack of suitable closely related plant models that offer a direct contrast between desiccation tolerance and sensitivity has hampered progress. We have assembled high-quality genomes for two closely related grasses, the desiccation-tolerant Sporobolus stapfianus and the desiccation-sensitive Sporobolus pyramidalis . Both species are complex polyploids; S. stapfianus is primarily tetraploid, and S. pyramidalis is primarily hexaploid. S. pyramidalis undergoes a major transcriptome remodeling event during initial exposure to dehydration, while S. stapfianus has a muted early response, with peak remodeling during the transition between 1.5 and 1.0 grams of water (gH 2 O) g −1 dry weight (dw). Functionally, the dehydration transcriptome of S. stapfianus is unrelated to that for S. pyramidalis . A comparative analysis of the transcriptomes of the hydrated controls for each species indicated that S. stapfianus is transcriptionally primed for desiccation. Cross-species comparative analyses indicated that VDT likely evolved from reprogramming of desiccation tolerance mechanisms that evolved in seeds and that the tolerance mechanism of S. stapfianus represents a recent evolution for VDT within the Chloridoideae. Orthogroup analyses of the significantly differentially abundant transcripts reconfirmed our present understanding of the response to dehydration, including the lack of an induction of senescence in resurrection angiosperms. The data also suggest that failure to maintain protein structure during dehydration is likely critical in rendering a plant desiccation sensitive. 

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