A Point Mutation in Phytochromobilin synthase Alters the Circadian Clock and Photoperiodic Flowering of Medicago truncatula

Abstract

Plants use seasonal cues to initiate flowering at an appropriate time of year to ensure optimal reproductive success. The circadian clock integrates these daily and seasonal cues with internal cues to initiate flowering. The molecular pathways that control the sensitivity of flowering to photoperiods (daylengths) are well described in the model plant Arabidopsis. However, much less is known for crop species, such as legumes. Here, we performed a flowering time screen of a TILLING population of Medicago truncatula and found a line with late-flowering and altered light-sensing phenotypes. Using RNA sequencing, we identified a nonsense mutation in the Phytochromobilin synthase (MtPΦBS) gene, which encodes an enzyme that carries out the final step in the biosynthesis of the chromophore required for phytochrome (phy) activity. The analysis of the circadian clock in the MtpΦbs mutant revealed a shorter circadian period, which was shared with the MtphyA mutant. The MtpΦbs and MtphyA mutants showed downregulation of the FT floral regulators MtFTa1 and MtFTb1/b2 and a change in phase for morning and night core clock genes. Our findings show that phyA is necessary to synchronize the circadian clock and integration of light signalling to precisely control the timing of flowering.

Gene-edited Mtsoc1 triple mutant Medicago plants do not flower

“…Nevertheless, progress has been made in identifying Medicago flowering-time regulators using forward and reverse genetics. These include the LD activators MtPHYTOCHROME A ( Jaudal et al., 2020b ), MtFE ( Thomson et al., 2021 ), and MtPHYTOCHROMOBILIN SYNTHASE ( Perez-Santangelo et al., 2022 ), and repressors MtCYCLING DOF FACTORS genes ( Zhang et al., 2019 ). The polycomb repressive complex 2 component MtVERNALISATION2 represses Medicago flowering until after vernalization ( Jaudal et al., 2016 ).…”

A Novel 10-Base Pair Deletion in the First Exon of GmHY2a Promotes Hypocotyl Elongation, Induces Early Maturation, and Impairs Photosynthetic Performance in Soybean

“…Kohchi et al (2001) initially reported the long-hypocotyl mutation of the HY2 gene encoding PΦB synthetase in Arabidopsis [10]. Subsequently, abnormal PΦB synthase function was reported in various other species, including the pcd2 mutant in pea (Pisum sativum L.) [11], the se13 mutant in rice (Oryza sativa L.) [12], the elh1 mutant in cucumber (Cucumis sativus L.) [13], the Gmlin1 mutant in soybean [14], and the Mtpφbs mutant in alfalfa (Medicago truncatula) [15]. Studies have shown that chromophore-deficient mutants generally have a light green or yellowish leaf phenotype, accompanied by a reduction in chlorophyll.…”