Increasing global temperatures have an impact on flowering, and the underlying mechanisms are just beginning to be unravelled(1,2). Elevated temperatures can induce flowering, and different mechanisms that involve either activation or de-repression of FLOWERING LOCUS T (FT) by transcription factor PHYTOCHROME INTERACTING FACTOR 4 (PIF4) or the FLOWERING LOCUS M (FLM)-SHORT VEGETATIVE PHASE (SVP) complex, respectively, have been suggested to be involved(3-6). Thermosensitivity in flowering has been mapped to FLM(5), which encodes a floral repressor(7,8). FLM undergoes alternative splicing(8) and it has been suggested that temperature-dependent alternative splicing leads to differential accumulation of the FLM-β and FLM-δ transcripts, encoding proteins with antagonistic effects, and that their ratio determines floral transition(4). Here we show that high temperatures downregulate FLM expression by alternative splicing coupled with nonsense-mediated mRNA decay (AS-NMD). We identify thermosensitive splice sites in FLM and show that the primary effect of temperature is explained by an increase in NMD target transcripts. We also show that flm is epistatic to pif4, which suggests that most of the PIF4 effects are FLM dependent. Our findings suggest a model in which the loss of the floral repressor FLM occurs through mRNA degradation in response to elevated temperatures, signifying a role for AS-NMD in conferring environmental responses in plants.

Most strains of the widespread endosymbiotic bacterium Wolbachia pipientis are benign or behave as reproductive parasites. The pathogenic strain wMelPop is a striking exception, however: it overreplicates in its insect hosts and causes severe life shortening. The mechanism of this pathogenesis is currently unknown. We have sequenced the genomes of three variants of wMelPop and of the closely related nonpathogenic strain wMelCS. We show that the genomes of wMelCS and wMelPop appear to be identical in the nonrepeat regions of the genome and differ detectably only by the triplication of a 19-kb region that is unlikely to be associated with life shortening, demonstrating that dramatic differences in the host phenotype caused by this endosymbiont may be the result of only minor genetic changes. We also compare the genomes of the original wMelPop strain from Drosophila melanogaster and two sequential derivatives, wMelPop-CLA and wMelPop-PGYP. To develop wMelPop as a novel biocontrol agent, it was first transinfected into and passaged in mosquito cell lines for approximately 3.5 years, generating wMelPop-CLA. This cell line-passaged strain was then transinfected into Aedes aegypti mosquitoes, creating wMelPop-PGYP, which was sequenced after 4 years in the insect host. We observe a rapid burst of genomic changes during cell line passaging, but no further mutations were detected after transinfection into mosquitoes, indicating either that host preadaptation had occurred in cell lines, that cell lines are a more selectively permissive environment than animal hosts, or both. Our results provide valuable data on the rates of genomic and phenotypic change in Wolbachia associated with host shifts over short time scales.

Insect-symbiont interactions are known to play key roles in host functions and fitness. The common insect endosymbiont Wolbachia can reduce the ability of several human pathogens, including arboviruses and the malaria parasite, to replicate in insect hosts. Wolbachia does not naturally infect Aedes aegypti, the primary vector of dengue virus, but transinfected Ae. aegypti have antidengue virus properties and are currently being trialled as a dengue biocontrol strategy. Here, we assess the impact of Wolbachia infection of Ae. aegypti on the microbiome of wild mosquito populations (adults and larvae) collected from release sites in Cairns, Australia, by profiling the 16S rRNA gene using next-generation sequencing. Our data indicate that Wolbachia reduces the relative abundance of a large proportion of bacterial taxa in Ae. aegypti adults, that is in accordance with the known pathogen-blocking effects of Wolbachia on a variety of bacteria and viruses. In adults, several of the most abundant bacterial genera were found to undergo significant shifts in relative abundance. However, the genera showing the greatest changes in relative abundance in Wolbachia-infected adults represented a low proportion of the total microbiome. In addition, there was little effect of Wolbachia infection on the relative abundance of bacterial taxa in larvae, or on species diversity (accounting for species richness and evenness together) detected in adults or larvae. These results offer insight into the effects of Wolbachia on the Ae. aegypti microbiome in a native setting, an important consideration for field releases of Wolbachia into the population.insect, microbiome, mosquito, symbiosis, Wolbachia | INTRODUCTIONInteractions between insect hosts and their associated microbiome can have substantial impact on host physiology. Broad changes to the microbiome can affect functions including development, fecundity, metabolism and immunity/susceptibility to pathogens (Coon, Vogel, Brown, & Strand, 2014;de O Gaio et al., 2011;Gall et al., 2016;Ridley, Wong, Westmiller, & Douglas, 2012). It is also well known that specific symbiotic bacteria of insects can play key roles in host functions (Douglas, 2011). Two well-studied systems include the aphids where the obligate symbiont Buchnera aphidicola synthesizes amino acids that are essential for aphid nutrition (Akman G€ und€ uz & Douglas, 2009) More broadly, the overall structure of the microbiome can also be important in the fitness of insects such as bees and mosquitoes, with changes to the composition of the microbiome shown to increase *These authors contributed equally to this study. the mortality of bees following exposure to bacterial pathogens (Raymann, Shaffer, & Moran, 2017) and to alter mosquito fecundity (de O Gaio et al., 2011;Gendrin et al., 2015;). It is evident in cases such as these where significant microbiome-host interactions occur, disturbing the insect bacterial population can adversely affect host fitness (Douglas, 2011). These include a recent study that has exami...

Plants are highly sensitive to environmental changes and even small variations in ambient temperature have severe consequences on their growth and development. Temperature affects multiple aspects of plant development, but the processes and mechanisms underlying thermo-sensitive growth responses are mostly unknown. Here we exploit natural variation in Arabidopsis thaliana to identify and characterize novel components and processes mediating thermo-sensitive growth responses in plants. Phenotypic screening of wild accessions identified several strains displaying pleiotropic growth defects, at cellular and organism levels, specifically at high ambient temperatures. Positional cloning and characterization of the underlying gene revealed that ICARUS1 (ICA1), which encodes a protein of the tRNAHis guanylyl transferase (Thg1) superfamily, is required for plant growth at high temperatures. Transcriptome and gene marker analyses together with DNA content measurements show that ICA1 loss-of-function results in down regulation of cell cycle associated genes at high temperatures, which is linked with a block in G2/M transition and endoreduplication. In addition, plants with mutations in ICA1 show enhanced sensitivity to DNA damage. Characterization of additional strains that carry lesions in ICA1, but display normal growth, shows that alternative splicing is likely to alleviate the deleterious effects of some natural mutations. Furthermore, analyses of worldwide and regional collections of natural accessions indicate that ICA1 loss-of-function has arisen several times independently, and that these occur at high frequency in some local populations. Overall our results suggest that ICA1-mediated-modulation of fundamental processes such as tRNAHis maturation, modify plant growth responses to temperature changes in a quantitative and reversible manner, in natural populations.

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