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1. Variation in seasonal timing traits and life history along a latitudinal transect in Mimulus ringens

   https://doi.org/10.1111/jeb.13941  

   Vest, Kelly; Sobel, James M. (October 2021, Journal of Evolutionary Biology)

   Abstract Seasonal timing traits are commonly under recurrent, spatially variable selection, and are therefore predicted to exhibit clinal variation. Temperate perennial plants often require vernalization to prompt growth and reproduction; however, little is known about whether vernalization requirements change across the range of a broadly distributed species. We performed a critical vernalization duration study inMimulus ringens, coupled with population genomic analysis. Plants from eight populations spanning the latitudinal range were exposed to varying durations of 4°C vernalization between 0 and 56 days, and flowering response was assessed. RADSeq was also performed to generate 1179 polymorphic SNPs, which were used to examine population structure. We found unexpected life history variation, with some populations lacking vernalization requirement. Population genomic analyses show that these life history variants are highly divergent from perennials, potentially revealing a cryptic species. For perennial populations, minimum vernalization time was surprisingly consistent. However, once vernalized, northern populations flowered almost 3 weeks faster than southern. Furthermore, southern populations exhibited sensitivity to vernalization times beyond flowering competency, suggesting an ability to respond adaptively to different lengths of winter.Mimulus ringens, therefore, reveals evidence of clinal variation, and provides opportunities for future studies addressing mechanistic and ecological hypotheses both within and between incipient species. 

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2. Transcriptome and epigenome analyses of vernalization in Arabidopsis thaliana

   https://doi.org/10.1111/tpj.14817  

   Xi, Yanpeng; Park, Sung‐Rye; Kim, Dong‐Hwan; Kim, Eun‐Deok; Sung, Sibum (June 2020, The Plant Journal)

   Summary Vernalization accelerates flowering after prolonged winter cold. Transcriptional and epigenetic changes are known to be involved in the regulation of the vernalization response. Despite intensive applications of next‐generation sequencing in diverse aspects of plant research, genome‐wide transcriptome and epigenome profiling during the vernalization response has not been conducted. In this work, to our knowledge, we present the first comprehensive analyses of transcriptomic and epigenomic dynamics during the vernalization process inArabidopsis thaliana. Six major clusters of genes exhibiting distinctive features were identified. Temporary changes in histone H3K4me3 levels were observed that likely coordinate photosynthesis and prevent oxidative damage during cold exposure. In addition, vernalization induced a stable accumulation of H3K27me3 over genes encoding many development‐related transcription factors, which resulted in either inhibition of transcription or a bivalent status of the genes. Lastly,FLC‐like andVIN3‐like genes were identified that appear to be novel components of the vernalization pathway. 

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3. EARLY FLOWERING 3 and Photoperiod Sensing in Brachypodium distachyon

   https://doi.org/10.3389/fpls.2021.769194  

   Bouché, Frédéric; Woods, Daniel P.; Linden, Julie; Li, Weiya; Mayer, Kevin S.; Amasino, Richard M.; Périlleux, Claire (January 2022, Frontiers in Plant Science)

   The proper timing of flowering, which is key to maximize reproductive success and yield, relies in many plant species on the coordination between environmental cues and endogenous developmental programs. The perception of changes in day length is one of the most reliable cues of seasonal change, and this involves the interplay between the sensing of light signals and the circadian clock. Here, we describe a Brachypodium distachyon mutant allele of the evening complex protein EARLY FLOWERING 3 (ELF3). We show that the elf3 mutant flowers more rapidly than wild type plants in short days as well as under longer photoperiods but, in very long (20 h) days, flowering is equally rapid in elf3 and wild type. Furthermore, flowering in the elf3 mutant is still sensitive to vernalization, but not to ambient temperature changes. Molecular analyses revealed that the expression of a short-day marker gene is suppressed in elf3 grown in short days, and the expression patterns of clock genes and flowering time regulators are altered. We also explored the mechanisms of photoperiodic perception in temperate grasses by exposing B. distachyon plants grown under a 12 h photoperiod to a daily night break consisting of a mixture of red and far-red light. We showed that 2 h breaks are sufficient to accelerate flowering in B. distachyon under non-inductive photoperiods and that this acceleration of flowering is mediated by red light. Finally, we discuss advances and perspectives for research on the perception of photoperiod in temperate grasses. 

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4. Expression of Concern: PHYTOCHROME C regulation of photoperiodic flowering via PHOTOPERIOD1 is mediated by EARLY FLOWERING 3 in Brachypodium distachyon

   https://doi.org/10.1371/journal.pgen.1010955  

   Woods D P; Li, W; Sibout, R; Shao, M; Laudencia-Chingcuanco, D; Vogel, J P; Dubcovsky, J; Amasino, R M (September 2023, PLOS Genetics)

   Köhler, C (Ed.)

   Daylength sensing in many plants is critical for coordinating the timing of flowering with the appropriate season. Temperate climate-adapted grasses such as Brachypodium distachyon flower during the spring when days are becoming longer. The photoreceptor PHYTOCHROME C is essential for long-day (LD) flowering in B. distachyon. PHYC is required for the LD activation of a suite of genes in the photoperiod pathway including PHOTOPERIOD1 (PPD1) that, in turn, result in the activation of FLOWERING LOCUS T (FT1)/FLORIGEN, which causes flowering. Thus, B. distachyon phyC mutants are extremely delayed in flowering. Here we show that PHYC-mediated activation of PPD1 occurs via EARLY FLOWERING 3 (ELF3), a component of the evening complex in the circadian clock. The extreme delay of flowering of the phyC mutant disappears when combined with an elf3 loss-of-function mutation. Moreover, the dampened PPD1 expression in phyC mutant plants is elevated in phyC/elf3 mutant plants consistent with the rapid flowering of the double mutant. We show that loss of PPD1 function also results in reduced FT1 expression and extremely delayed flowering consistent with results from wheat and barley. Additionally, elf3 mutant plants have elevated expression levels of PPD1, and we show that overexpression of ELF3 results in delayed flowering associated with a reduction of PPD1 and FT1 expression, indicating that ELF3 represses PPD1 transcription consistent with previous studies showing that ELF3 binds to the PPD1 promoter. Indeed, PPD1 is the main target of ELF3-mediated flowering as elf3/ppd1 double mutant plants are delayed flowering. Our results indicate that ELF3 operates downstream from PHYC and acts as a repressor of PPD1 in the photoperiod flowering pathway of B. distachyon. 

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5. Diverse Developmental Responses to Warming Temperatures Underlie Changes in Flowering Phenologies

   https://doi.org/doi:10.1093/icb/icz076  

   Diggle, Pamela K.; Mulder, Christa P. (October 2019, Integrative and comparative biology)

   Climate change has resulted in increased temperature means across the globe. Many angiosperms flower earlier in response to rising temperature and the phenologies of these species are reasonably well predicted by models that account for spring (early growing season) and winter temperatures. Surprisingly, however, exceptions to the general pattern of precocious flowering are common. Many species either do not appear to respond or even delay flowering in, or following, warm growing seasons. Existing phenological models have not fully addressed such exceptions to the common association of advancing phenologies with warming temperatures. The phenological events that are typically recorded (e.g., onset of flowering) are but one phase in a complex developmental process that often begins one or more years previously, and flowering time may be strongly influenced by temperature over the entire multi-year course of flower development. We propose a series of models that explore effects of growing-season temperature increase on the multiple processes of flower development and how changes in development may impact the timing of anthesis. We focus on temperate forest trees, which are characterized by preformation, the initiation of flower primordia one or more years prior to anthesis. We then synthesize the literature on flower development to evaluate the models. Although fragmentary, the existing data suggest the potential for temperature to affect all aspects of flower development in woody perennials. But, even for relatively well studied taxa, the critical developmental responses that underlie phenological patterns are difficult to identify. Our proposed models explain the seemingly counter-intuitive observations that warmer growingseason temperatures delay flowering in many species. Future research might concentrate on taxa that do not appear to respond to temperature, or delay flowering in response to warm temperatures, to understand what processes contribute to this pattern. 

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