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The transcriptomic response to a short day to long day shift in the reference legume Medicago truncatula

ABSTRACT: Photoperiod regulated flowering is a well understood developmental pathway in the intensively studied Brassicaceae species Arabidopsis thaliana and in the monocot rice, but less so in other angiosperm groups. One such group, the temperate legumes in the Fabaceae family which are important both agriculturally and ecologically, accelerate their flowering in response to long-day photoperiods (LD), but lack functional homologues of key regulatory genes present in A. thaliana such as CO. Curiously previous work in the reference legume Medicago truncatula has shown that floral activator MtFTa1, which is upregulated by LD and vernalisation, does not exhibit a peak in expression at dusk like its homologue in A. thaliana FLOWERING LOCUS T, instead MtFTa1 maintains a near constant pattern of expression. In addition legumes possess for other FT-like genes such as the MtFTb genes expressed in LD which may also act in the regulation of flowering time. This study utilises RNA-Seq to identify genes which may regulate or be co-expressed with these FT-like genes in Medicago truncatula. Following a shift from short-day photoperiods to inductive long-days genes which alter their pattern of expression are distinguished from those which just alter their magnitude of expression (and those that do neither). Specifically this study focuses on the first few hours of the day in the young leaves which coincides with the first diurnal peak of the FTb genes. It goes on to categorise these genes into groups with similar patterns of expression using c-means clustering. In the process this study identifies a number of potential candidate genes for future studies to consider.

ORGANISM(S): Medicago truncatula

PROVIDER: GSE118893 | GEO | 2018/08/23

REPOSITORIES: GEO

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Project description:Optimised flowering time is an important trait ensuring successful plant adaptation and crop productivity. SOC1-like genes encode MADS transcription factors known to play important roles in flowering control in many plants. This includes the best characterised eudicot model Arabidopsis thaliana (Arabidopsis) where SOC1 promotes flowering and functions as a floral integrator gene integrating signals from different flowering time regulatory pathways. Medicago truncatula (Medicago) is a temperate reference legume with strong genomic and genetic resources used to study flowering pathways in legumes. Interestingly, despite responding to the similar floral-inductive cues of extended cold (vernalisation) followed by warm long days, as winter annual Arabidopsis, Medicago lacks FLC and CO which are key regulators of flowering in Arabidopsis. Unlike Arabidopsis with one SOC1 gene, multiple gene duplication events have given rise to three MtSOC1 paralogs within the Medicago genus in legumes; one Fabaceae group A SOC1 gene, MtSOC1a, and two tandemly-repeated Fabaceae group B SOC1 genes, MtSOC1b and MtSOC1c. Previously, we showed that MtSOC1a has unique functions in floral promotion in Medicago. The Mtsoc1a Tnt1 retroelement insertion single mutant showed moderately delayed flowering in long and short day photoperiods, with and without prior vernalization, compared with wild type. On the other hand, Mtsoc1b Tnt1 single mutants did not have altered flowering time or flower development, indicating that it was redundant in an otherwise wild type background. Here, we describe the generation of Mtsoc1 triple mutant plants by CRISPR-Cas9 gene editing. Two independent Mtsoc1 homozygous triple mutants were non-flowering and bushy in floral inductive VLD. Phenotyping and gene expression analyses by RNA-seq and RT-qPCR indicate that the Mtsoc1 triple mutants remain vegetative. Thus overall, the Mtsoc1 triple mutants are dramatically different from the single Mtsoc1a mutant and the Arabidopsis soc1 mutant; implicating multiple MtSOC1 genes in critical overlapping roles in the transition to flowering in Medicago.

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The transcriptomic response to a short day to long day shift in the reference legume Medicago truncatula

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