MOLECULAR BASES OF PLANT DEVELOPMENTAL PHASE TRANSITIONS
- Abelenda Vila, Jose A. - Young Investigator Researcher (YIR)
- Álvarez Aragón, Rocío - Postdoctoral Fellow
- Barrero Gil, Javier - Postdoctoral Fellow
- Bouza Morcillo, Laura - Postdoctoral Fellow
- Calleja Cabrera, Julián - Postdoctoral Fellow
- Calvo Martín, Ana - PhD Student
- Carrera Castaño, Gerardo - Postdoctoral Fellow
- Curci, Martina - PhD Student
- Fernández Rodríguez, Pedro - Technician
- Guillem Bernal, María - PhD Student
- Pozas Castañares, Jenifer - Technician
- Yingnan, Tian - PhD Student
During their life cycle plants undergo different developmental phases, including embryonic, vegetative and reproductive development. These developmental stages are characterised by specific patterns of cellular differentiation. The switch from a developmental phase to the next is under the control of spatial and temporal patterns of gene expression, so that selective activation or silencing of genes directs plant development through different phase changes. Our group is focused on understanding different molecular mechanisms involved in the regulation of plant developmental transitions. In particular, we are interested in a couple of phase transitions: flowering and seed germination/seedling establishment, with adaptive value for plant species as well as a significant impact on crop yield.
Since epigenetic processes are key players in the regulation of plant development and chromatin represents the interphase mediating genome interaction with the environment, the characterization of chromatin-mediated regulatory processes represents a corner stone in our investigations. Our current research directions are devoted to dissect the role of chromatin remodeling in the regulation of plant development, focusing on the role of the histone acetyltransferase (HAT) complex NuA4 (NuA4-C) in the regulation of flowering time and other developmental processes in Arabidopsis like chloroplast biogenesis during the transition from heterotrophic to autotrophic growth (Gomez-Zambrano et al., 2018; Crevillen et al., 2019; Espinosa-Cores et al., 2020; Barrero-Gil et al., 2021; Barrero-Gil et al., 2022). Our results show that different NuA4-C subunits may perform distinct functions in the flowering response to environmental cues such as photoperiod or ambient temperature. Also, mutants affected in particular subunits of NuA4-C display specific phenotypic alterations regarding other developmental traits or environmental responses. We are focused on elucidating the molecular basis for specific responses of Piccolo NuA4-C subunits. Furthermore, we are expanding the characterization of the two Arabidopsis HAM homologs using genomic approaches to further delve into the role of the NuA4-C catalytic subunit in the control of plant development. Since HAM proteins are present in additional chromatin remodeling complexes, the comparative analysis with other subunits of this HAT complex will also shed light on NuA4-C-dependent and -independent roles of HAM proteins. Altogether, these analyses will enlighten the relevance of histone acetylation in the regulation of plant development. Furthermore, our recent work revealed a novel attenuation mechanism of stress responses during the flowering initiation mediated by the MRG subunits of NuA4-C (Barrero-Gil et al., 2021). Under our CEPEI´s CHROPTIPLANT initiative, we are further exploring the basis for this epigenetic switch likely involved in the optimization of plant reproduction and fitness at the expense of costly responses to environmental challenges.
In addition, with the goal of assisting the agrifood sector in developing crops better suited to withstand increasing environmental temperature, we are analyzing plant developmental responses to warm ambient temperature in Brassica crops. Our analyses have identified several differentially expressed genes in Brassica napus (oilseed rape, OSR) varieties displaying differential flowering responses to warmth (Abelenda et al., 2023). We are currently characterizing at the functional level factors that could mediate plant developmental responses to temperature through chromatin reorganization. In parallel, we are following similar approaches in the PRIMA´s project BrasExplor involving B. rapa (turnips) (Del Olmo et al., 2019) and B. oleracea (cabbage, cauliflower), focused on the wide exploration of genetic diversity in Brassica species for sustainable crop production. Finally, in the EpiSeedLink MSCA-Doctoral Network we are addressing at the molecular level the effects that the exposure of mother plants to warm ambient temperature has on the performance of OSR seeds during germination and seedling establishment, two key developmental stages influencing crop yield. Environmental conditions experienced by mother plants affect seed performance in the progeny, and chromatin remodeling processes are likely involved in this memory. We are interested in identifying molecular and epigenetic mechanisms underlying plant responses to temperature, with the overarching goal of contributing to enhance crop resilience to suboptimal environments.
Recent relevant results
The deposition of histone variant H2A.Z and histone acetylation mediate different aspects of chromatin function and modulate flowering responses in Arabidopsis
During recent years our lab has analyzed epigenetic mechanisms that participate in the regulation of the floral transition through the molecular and genetic characterization of several Arabidopsis subunits (ARP6, SWC6) of the plant SWR1 chromatin remodeling complex, which catalyzes the exchange of H2A histone by the H2A.Z variant and that regulates flowering time in plants (Jarillo & Piñeiro, 2015). In addition, we have studied AtSWC4 and AtYAF9-like proteins, whose yeast orthologues are present in the SWR1 complex and are shared by the HAT complex NuA4 (Espinosa-Cores et al., 2020), indicating a possible functional interplay between these two complexes. Remarkably, we have shown that SWC4 participates in the recruitment of the SWR1 complex and H2A.Z deposition to modulate gene expression through the specific binding to AT-rich elements in regulatory regions of target genes such as the floral integrator FT (Gómez-Zambrano et al., 2018). We have also demonstrated that Arabidopsis YAF9 histone readers modulate flowering time through NuA4-complex-dependent H4 and H2A.Z histone acetylation at FLC chromatin (Crevillen et al., 2019).
Functions of the putative NuA4 subunits in different plant biological responses.
A chromatin switch attenuates abiotic stress responses during the floral transition
While stress conditions are known to impact plant development, how developmental transitions influence plant responses to adverse conditions has not been addressed, and the molecular mechanisms underlying the integration of plant development with stress responses remain obscure. We have revealed a novel molecular mechanism of stress response attenuation during the onset of flowering in Arabidopsis (Barrero-Gil et al., 2021). This mechanism involves NuA4 proteins (MRGs) that bind methylated forms of histone H3 and function as a chromatin switch on the floral integrator gene SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) to coordinate flowering initiation with plant responsiveness to hostile environments. These chromatin proteins are required to directly activate SOC1 expression during flowering induction by promoting histone H4 acetylation. In turn, SOC1 represses a broad array of genes that mediate abiotic stress responses such as cold or drought tolerance. The results obtained indicate that during the transition from vegetative to reproductive growth, this epigenetic switch that acts on SOC1 constitutes a central hub in a mechanism that tunes down stress responses to enhance reproductive success and plant fitness at the expense of costly efforts for adaptation to challenging environments.
Hypothetical working model showing how MRG-mediated chromatin acetylation at the SOC1 locus
coordinates the floral transition and abiotic stress responses
How chromatin contributes to make plants green: Unveiled a NuA4-mediated histone acetylation mechanism regulating Arabidopsis chloroplast biogenesis
Photomorphogenic changes encompass a wide range of responses including the differentiation of non-photosynthetic plastids into chloroplasts, a crucial step in the transition from heterotrophic to autotrophic growth in plants. This process is light-induced and relies on the orchestrated transcription of nuclear and plastid genes, enabling the effective assembly and regulation of the photosynthetic machinery. Our group has revealed a novel regulation level for this process by unveiling the involvement of chromatin remodelling in the nuclear control of plastid gene expression for proper chloroplast biogenesis and function (Barrero-Gil et al., 2022). The two Arabidopsis homologs of the yeast EPL1 protein, components of the NuA4 histone acetyltransferase complex, are essential for plastid transcription and correct chloroplast development and performance. We showed that EPL1 proteins are light-regulated and necessary for concerted expression of nuclear genes encoding most components of chloroplast transcriptional machinery, directly mediating H4K5ac deposition at these loci and promoting the expression of plastid genes required for chloroplast biogenesis. These data unveil a NuA4-mediated mechanism regulating chloroplast biogenesis that links the transcription of nuclear and plastid genomes during chloroplast development.
Working model of light-induction of chloroplast biogenesis showing how NuA4-C coordinates nuclear and plastid gene expression during this process by promoting H4 acetylation in the regulatory regions of genes that are crucial for plastid transcription.
Securing yield stability of Brassica crops in changing climate conditions
Elevated growth temperatures associated with climate change impact growth and flowering time and affect crop productivity by increasing yield losses. Oilseed rape is a premium oilseed crop also threatened by growing ambient temperatures. To shed light on the oilseed rape vegetative to reproductive phase transition under warm temperatures, our group took advantage of the diverse flowering responses of oilseed rape spring cultivated varieties at different temperature regimes. The current model for flowering response to warm temperature in Arabidopsis hypothesizes that high-temperature induction of FT expression is caused by changes in chromatin accessibility after the eviction of H2A.Z-containing nucleosomes, although the exact mechanism is not well understood. Additionally, a working mechanism behind H2A.Z control of temperature-dependent flowering repression in Brassica rapa proposes that BraFT is repressed through H2A.Z accumulation under non-inductive high ambient temperature. Our results identified BnaFTA2 as a key candidate gene in temperature-dependent flowering control in oilseed rape. Furthermore, the variety displaying the earliest flowering time (Wesway), showed consistent differences in H2A.Z deposition in BnaFTA2 between 21ºC and 28ºC, in line with previous results in Arabidopsis and the observed flowering phenotype. However, we found no clear correlation between H2A.Z occupancy and BnaFTA2 repression in late flowering accessions under high-temperature, including the commonly used variety RV31. In addition, ChIP analysis in oilseed rape ARP6 RNAi silenced plants with low H2A.Z levels corroborates that BnaFTA2 expression is only slightly affected by the presence of this non-canonical histone. These observations led us to propose that high ambient temperature impacts oilseed rape flowering time through both H2A.Z-dependent and independent mechanisms. Our analyses will help to harness crop response mechanisms for improving adaptation under the current climatic scenario.
Flowering time characterisation of selected Brassica napus varieties.
Boter, M., Pozas, J., Jarillo, J.A., Piñeiro, M., Pernas, M. 2023. Brassica napus Roots Use Different Strategies to Respond to Warm Temperatures. International Journal of Molecular Sciences 24,1143. DOI: 10.3390/ijms24021143
Abelenda, J.A., Trabanco, N., Olmo, I. del, Pozas, J., Martín-Trillo, M. del M., Gómez-Garrido, J., Esteve-Codina, A., Pernas, M., Jarillo, J.A., Piñeiro, M. 2022. High ambient temperature impacts on flowering time in Brassica napus through both H2A.Z-dependent and independent mechanisms. Plant, Cell & Environment. DOI: 10.1111/pce.14526
Barrero-Gil, J., Bouza-Morcillo, L., Espinosa-Cores, L., Piñeiro, M., Jarillo, J.A. 2022. H4 acetylation by the NuA4 complex is required for plastid transcription and chloroplast biogenesis. Nature Plants 1–12. DOI: 10.1038/s41477-022-01229-4
Poza-Viejo, L., Payá-Milans, M., Martín-Uriz, P.S., Castro-Labrador, L., Lara-Astiaso, D., Wilkinson, M.D., Piñeiro, M., Jarillo, J.A., Crevillén, P. 2022. Conserved and distinct roles of H3K27me3 demethylases regulating flowering time in Brassica rapa. Plant, Cell & Environment n/a. DOI: 10.1111/pce.14258
Barrero-Gil, J., Mouriz, A., Piqueras, R., Salinas, J., Jarillo, J.A., Piñeiro, M. 2021. A MRG-operated chromatin switch at SOC1 attenuates abiotic stress responses during the floral transition. Plant Physiology. DOI: 10.1093/plphys/kiab275
Espinosa-Cores, L., Bouza-Morcillo, L., Barrero-Gil, J., Jiménez-Suárez, V., Lázaro, A., Piqueras, R., Jarillo, J.A., Piñeiro, M. 2020. Insights Into the Function of the NuA4 Complex in Plants. Frontiers in Plant Science 11, 125. DOI: 10.3389/fpls.2020.00125
del Olmo, I., Poza‐Viejo, L., Piñeiro, M., Jarillo, J.A., Crevillén, P. 2019. High ambient temperature leads to reduced FT expression and delayed flowering in Brassica rapa via a mechanism associated with H2A.Z dynamics. The Plant Journal. DOI: 10.1111/tpj.14446
Crevillén, P., Gómez‐Zambrano, Á., López, J.A., Vázquez, J., Piñeiro, M., Jarillo, J.A. 2019. Arabidopsis YAF9 histone readers modulate flowering time through NuA4-complex-dependent H4 and H2A.Z histone acetylation at FLC chromatin. New Phytologist. DOI: 10.1111/nph.15737
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