Flowering time runs hot and cold

CmARF3-CmTCP7 module regulates flowering time in chrysanthemum (Chrysanthemum morifolium)

The precise timing of flowering in response to environment plays a crucial role in the reproductive processes of plants. The FLOWERING LOCUS T (FT)-FD module is a well-established key node in the photoperiod-mediated pathway. However, the identity of novel partners involved in this network and its regulatory mechanisms remain elusive in most nonmodel species. Here, we found that TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR7 (CmTCP7) functions as a floral repressor in Chrysanthemum morifolium. Its upstream transcriptional regulator AUXIN RESPONSE FACTOR3 (CmARF3) promotes flowering by directly repressing CmTCP7 expression. The expression levels of both genes are short-day inducible. Interestingly, FLOWERING LOCUS T-like3 (CmFTL3) interacts with FD-like1 (CmFDL1), which activates flowering-accelerating gene Chrysanthemum Dendrathema MADS111-like (CmCDM111L). Meanwhile, CmTCP7 interacts with CmFTL3 and CmFDL1, delaying the CmFTL3 and CmFDL1 complex-promoted flowering in chrysanthemum "Jinba." These findings reveal a novel regulatory module controlling photoperiod-dependent flowering in chrysanthemum.

Shifts in vernalization and phenology at the rear edge hold insight into the adaptation of temperate plants to future milder winters

Temperate plants often regulate reproduction through winter cues, such as vernalization, that may decrease under climate change. Studies of rear-edge populations, glacial relicts that persist in environments that have warmed since the last glaciation, can provide insight into the adaptive potential to milder winters. We studied how rear-edge populations have adapted to shorter winters and compared them to the rest of the range in the herb Campanula americana. Using citizen science, climate data and experimental climate manipulation, we characterize variation in vernalization requirements and reproductive phenology across the range and their potential climatic drivers. Rear-edge populations experienced little to no vernalization in nature. In climate manipulation experiments, these populations also had a reduced vernalization requirement, a weaker response to changes in vernalization length and flowered later compared to the rest of the range. Our results suggest shifts in phenology and its underlying regulation at the rear edge to compensate for unreliable vernalization cues. Thus, future milder winters may be less detrimental to these populations than more northern ones. Furthermore, our results showcase strong adaptive shifts at the rear edge of temperate plants' ranges, highlighting the importance of these areas in studies of predicted future climates.

Historic rewiring of grass flowering time pathways and implications for crop improvement under climate change

Grasses are fundamental to human survival, providing a large percentage of our calories, fuel, and fodder for livestock, and an enormous global carbon sink. A particularly important part of the grass plant is the grain-producing inflorescence that develops in response to both internal and external signals that converge at the shoot tip to influence meristem behavior. Abiotic signals that trigger reproductive development vary across the grass family, mostly due to the unique ecological and phylogenetic histories of each clade. The time it takes a grass to flower has implications for its ability to escape harsh environments, while also indirectly affecting abiotic stress tolerance, inflorescence architecture, and grain yield. Here, we synthesize recent insights into the evolution of grass flowering time in response to past climate change, particularly focusing on genetic convergence in underlying traits. We then discuss how and why the rewiring of a shared ancestral flowering pathway affects grass yields, and outline ways in which researchers are using this and other information to breed higher yielding, climate-proof cereal crops.

Low temperature-mediated repression and far-red light-mediated induction determine morning FLOWERING LOCUS T expression levels

In order to flower in the appropriate season, plants monitor light and temperature changes and alter downstream pathways that regulate florigen genes such as Arabidopsis (Arabidopsis thaliana) FLOWERING LOCUS T (FT). In Arabidopsis, FT messenger RNA levels peak in the morning and evening under natural long-day conditions (LDs). However, the regulatory mechanisms governing morning FT induction remain poorly understood. The morning FT peak is absent in typical laboratory LDs characterized by high red:far-red light (R:FR) ratios and constant temperatures. Here, we demonstrate that ZEITLUPE (ZTL) interacts with the FT repressors TARGET OF EATs (TOEs), thereby repressing morning FT expression in natural environments. Under LDs with simulated sunlight (R:FR = 1.0) and daily temperature cycles, which are natural LD-mimicking environmental conditions, FT transcript levels in the ztl mutant were high specifically in the morning, a pattern that was mirrored in the toe1 toe2 double mutant. Low night-to-morning temperatures increased the inhibitory effect of ZTL on morning FT expression by increasing ZTL protein levels early in the morning. Far-red light counteracted ZTL activity by decreasing its abundance (possibly via phytochrome A (phyA)) while increasing GIGANTEA (GI) levels and negatively affecting the formation of the ZTL-GI complex in the morning. Therefore, the phyA-mediated high-irradiance response and GI play pivotal roles in morning FT induction. Our findings suggest that the delicate balance between low temperature-mediated ZTL activity and the far-red light-mediated functions of phyA and GI offers plants flexibility in fine-tuning their flowering time by controlling FT expression in the morning.

Unlocking Nature's Clock: CRISPR Technology in Flowering Time Engineering

Flowering is a crucial process in the life cycle of most plants as it is essential for the reproductive success and genetic diversity of the species. There are situations in which breeders want to expedite, delay, or prevent flowering, for example, to shorten or prolong vegetative growth, to prevent unwanted pollination, to reduce the risk of diseases or pests, or to modify the plant's phenotypes. This review aims to provide an overview of the current state of knowledge to use CRISPR/Cas9, a powerful genome-editing technology to modify specific DNA sequences related to flowering induction. We discuss the underlying molecular mechanisms governing the regulation of the photoperiod, autonomous, vernalization, hormonal, sugar, aging, and temperature signal pathways regulating the flowering time. In addition, we are investigating the most effective strategies for nominating target genes. Furthermore, we have collected a dataset showing successful applications of CRISPR technology to accelerate flowering in several plant species from 2015 up to date. Finally, we explore the opportunities and challenges of using the potential of CRISPR technology in flowering time engineering.

It is time to move: Heat-induced translocation events

Climate change-induced temperature fluctuations impact agricultural productivity through short-term intense heat waves or long-term heat stress. Plants have evolved sophisticated strategies to deal with heat stress. Understanding perception and transduction of heat signals from outside to inside cells is essential to improve plant thermotolerance. In this review, we will focus on translocation of molecules and proteins associated with signal transduction to understand how plant cells decode signals from the environment to trigger a suitable response.

Independent recruitment of FRUITFULL-like transcription factors in the convergent origins of vernalization-responsive grass flowering

Flowering in response to low temperatures (vernalization) has evolved multiple times independently across angiosperms as an adaptation to match reproductive development with the short growing season of temperate habitats. Despite the context of a generally conserved flowering time network, evidence suggests that the genes underlying vernalization responsiveness are distinct across major plant clades. Whether different or similar mechanisms underlie vernalization-induced flowering at narrower (e.g., family-level) phylogenetic scales is not well understood. To test the hypothesis that vernalization responsiveness has evolved convergently in temperate species of the grass family (Poaceae), we carried out flowering time experiments with and without vernalization in several representative species from different subfamilies. We then determined the likelihood that vernalization responsiveness evolved through parallel mechanisms by quantifying the response of Pooideae vernalization pathway FRUITFULL (FUL)-like genes to extended periods of cold. Our results demonstrate that vernalization-induced flowering has evolved multiple times independently in at least five grass subfamilies, and that different combinations of FUL-like genes have been recruited to this pathway on several occasions.

Nutrient-mediated modulation of flowering time

Nutrition affects plant growth and development, including flowering. Flowering represents the transition from the vegetative period to the reproduction period and requires the consumption of nutrients. Moreover, nutrients (e.g., nitrate) act as signals that affect flowering. Regulation of flowering time is therefore intimately associated with both nutrient-use efficiency and crop yield. Here, we review current knowledge of the relationships between nutrients (primarily nitrogen, phosphorus, and potassium) and flowering, with the goal of deepening our understanding of how plant nutrition affects flowering.

Convergent evolution of the annual life history syndrome from perennial ancestors

Despite most angiosperms being perennial, once-flowering annuals have evolved multiple times independently, making life history traits among the most labile trait syndromes in flowering plants. Much research has focused on discerning the adaptive forces driving the evolution of annual species, and in pinpointing traits that distinguish them from perennials. By contrast, little is known about how 'annual traits' evolve, and whether the same traits and genes have evolved in parallel to affect independent origins of the annual syndrome. Here, we review what is known about the distribution of annuals in both phylogenetic and environmental space and assess the evidence for parallel evolution of annuality through similar physiological, developmental, and/or genetic mechanisms. We then use temperate grasses as a case study for modeling the evolution of annuality and suggest future directions for understanding annual-perennial transitions in other groups of plants. Understanding how convergent life history traits evolve can help predict species responses to climate change and allows transfer of knowledge between model and agriculturally important species.