High ambient temperature impacts on flowering time in Brassica napus through both H2A.Z‐dependent and independent mechanisms

Abstract

Knowledge concerning the integration of genetic pathways mediating the responses to environmental cues controlling flowering initiation in crops is scarce. Here, we reveal the diversity in oilseed rape (OSR) flowering response to high ambient temperature. Using a set of different spring OSR varieties, we found a consistent flowering delay at elevated temperatures.Remarkably, one of the varieties assayed exhibited the opposite behaviour. Several FT-like paralogs are plausible candidates to be part of the florigen in OSR. We revealed that BnaFTA2 plays a major role in temperature-dependent flowering initiation. Analysis of the H2A.Z histone variant occupancy at this locus in different Brassica napus varieties produced contrasting results, suggesting the involvement of additional molecular mechanisms in BnaFTA2 repression at high ambient temperature. Moreover, BnARP6 RNAi plants showed little accumulation of H2A.Z at high temperature while maintaining temperature sensitivity and delayed flowering. Furthermore, we found that H3K4me3 present in BnaFTA2 under inductive flowering conditions is reduced at high temperature, suggesting a role for this hallmark of transcriptionally active chromatin in the OSR flowering response to warming. Our work emphasises the plasticity of flowering responses in B. napus and offers venues to optimise this process in crop species grown under suboptimal environmental conditions.

Complex regulation of flowering by high temperatures

“…In this sense, it is not surprising that different plants may utilize distinct transcription factors employing unique sets of epigenetic modifications to achieve proper FT regulation at high temperatures. Indeed, in their study, Abelenda et al (2023) have found that the promoter of BnaFTA2 (where transcription factors normally bind) is responsible for its regulation by high temperatures, and the levels of chromatin accessibility and H3K4me3 at the BnaFTA2 locus positively correlate with its expression changes. Key basic knowledge breakthroughs in understanding thermal regulation of flowering will be made by identifying transcription factors that directly control thermal‐mediated FT transcription in different plant species, followed by characterizing their regulatory mechanisms.…”

“…The reason for diversification in flowering responses to high temperatures is not clear, and it may be attributed to plant‐specific growth habits, life cycles, and breeding backgrounds that eventually differentiate the regulatory mechanisms of flowering by high temperatures. Nevertheless, studies so far all suggest a central role of FT ‐like genes in integrating thermal signals, as works in Arabidopsis and several other plant species have demonstrated that changes in transcript levels of FT ‐like genes always correlate with flowering phenotypes induced by high temperatures (Abelenda et al, 2023; del Olmo et al, 2019; Kumar and Wigge, 2010; Nakano et al, 2013; Noy‐Porat et al, 2013). These results highlight the importance of transcriptional regulation of FT ‐like genes in thermal‐controlled flowering.…”

“…FLOWERING LOCUS T (FT) is an evolutionarily and functionally conserved floral integrator that promotes flowering (Putterill and Varkonyi‐Gasic, 2016). Abelenda et al (2023) reasoned that FT ‐like genes are normally expressed at low levels and with diurnal patterns, and their expression differences may not be well reflected in transcriptome analysis. Therefore, they focused on FT ‐like genes for detailed analyses and eventually identified BnaFTA2 as a main candidate accountable for differential flowering regulation by high temperatures in B. napus .…”

“…Although studies with a wide range of British and Massachusetts (USA) plant species suggest that climate warming is generally associated with flowering acceleration (Fitter and Fitter, 2002;Miller-Rushing and Primack, 2008), some others investigating individual plant species and their accessions have found that temperature elevation may promote, delay or have only little effect on flowering (Table 1). In this issue of Plant, Cell & Environment, Abelenda et al (Abelenda et al, 2023) B. napus is a leading oil crop that originated from the hybridization between Brassica rapa (AA) and Brassica oleracea (CC) (Lu et al, 2019). The authors started their investigation by taking several spring B. napus cultivars to measure their flowering time under optimal (21°C) and high (28°C) temperatures.…”

Advances in biological functions and mechanisms of histone variants in plants

“…Further studies reveal that the INO80 complex mediates the eviction of H2A.Z and consequently activates the expressions of thermo-responsive genes, thereby contributing thermal morphogenesis of Arabidopsis ( Xue et al, 2021 ). Heat stress regulates plant flowering time by altering the deposition of H2A.Z on FT gene, whereas this regulatory effect is specific in different plant species ( Del Olmo et al, 2019 ; Abelenda et al, 2023 ). In conclusion, current researches on functions of histone variants in plants response to stresses have been focused on the H2A variants, and further investigations are needed to reveal the functions of other histone variants.…”