With global climate change, water scarcity threatens whole agro/ecosystems. The desert moss Syntrichia caninervis, an extremophile, offers novel insights into surviving desiccation and heat. The sequenced S. caninervis genome consists of 13 chromosomes containing 16 545 protein-coding genes and 2666 unplaced scaffolds. Syntenic relationships within the S. caninervis and Physcomitrella patens genomes indicate the S. caninervis genome has undergone a single whole genome duplication event (compared to two for P. patens) and evidence suggests chromosomal or segmental losses in the evolutionary history of S. caninervis. The genome contains a large sex chromosome composed primarily of repetitive sequences with a large number of Copia and Gypsy elements. Orthogroup analyses revealed an expansion of ELIP genes 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.

Our data suggest that both male-biased mortality and sexual dimorphism in thresholds for sex expression could explain genetic and phenotypic sex ratio biases and that phenotypic sex expression alone over-estimates the extent of actual sex ratio bias present in these two populations of .

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PREMISE Desiccation tolerance (DT) is a widespread phenomenon among land plants, and variable ecological strategies for DT are likely to exist. Using Syntrichia 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. METHODS 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 (RoDmin) at RHeq = 42% that did not elicit damage 24 h postrehydration. RESULTS DT strategy varied with life phase, with adult shoots having the lowest RoDmin (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 highest RHeq used (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 the RHeq, thus implicating damage. CONCLUSIONS Life phases of the moss S. caninervis had 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.

Desiccation tolerance is a complex trait that is broadly but infrequently present throughout the evolutionary tree of life. Desiccation tolerance has played a significant role in land plant evolution, in both the vegetative and reproductive life history stages. In the land plants, the late embryogenesis abundant (LEA) gene families are involved in both abiotic stress tolerance and the development of reproductive propagules. They are also a major component of vegetative desiccation tolerance. Phylogenies were estimated for four families of LEA genes from Arabidopsis, Physcomitrella, and the desiccation tolerant plants Tortula ruralis, Craterostigma plantagineum, and Xerophyta humilis. Microarray expression data from Arabidopsis and a subset of the Physcomitrella LEAs were used to estimate ancestral expression patterns in the LEA families and to evaluate alternative hypotheses for the origins of vegetative desiccation tolerance in the flowering plants. The results contradict the idea that vegetative desiccation tolerance in the resurrection angiosperms Craterostigma and Xerophyta arose through the co-option of genes exclusively related to stress tolerance, and support the propagule-derived origin of vegetative desiccation tolerance in the resurrection plants.

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Premise of research: Natural populations of many mosses appear highly female-biased based on the presence of reproductive structures. This bias could be caused by increased male mortality, lower male growth rate, or a higher threshold for achieving sexual maturity in males. Here we test these hypotheses using samples from two populations of the Mojave Desert moss Syntrichia caninervis.Methods: We used double digest restriction-site associated DNA (RAD) sequencing to identify candidate sex-associated loci in a panel of sex-expressing plants. Next, we used putative sex-associated markers to identify the sex of individuals without sex structures.Key results: We found an 18:1 phenotypic female: male sex ratio in the higher elevation site (Wrightwood), and no sex expression at the low elevation site (Phelan). In contrast, based on genetic data we found a 2:1 female bias in the Wrightwood site and only females in the Phelan site. The area occupied by male and female genets was indistinguishable.Conclusions: These data suggest that both differential mortality and sexual dimorphism in thresholds for sex expression likely contribute to population genetic and phenotypic sex ratio biases, and that phenotypic sex expression alone fails to capture the extent of actual sex ratio bias present in natural populations of S. caninervis.

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