Cloning And Functional Study Of Soybean Phytochrome Genes

Plants possess a series of photoreceptors to respond to the light signal. One of the important kinds of photoreceptors is called phytochromes, which are essential for red and far-red light sensing and involved in seed germination, photomorphogenesis, shade avoidance, flowering, and many other developmental events.In present research, two PHYTOCHROME A (PHYA) homologous genes and two PHYTOCHROME B (PHYB) homologous genes are cloned from the soybean (Glycine max L. Merr.) cultivar Kennong18, and are named as GmPHYA1, GmPHYA2, GmPHYB1, and GmPHYB2, respectively. Bioinformatics analysis reveals that GmPHYA1and GmPHYA2shared94%similarity in amino acid sequences and95%for GmPHYB1and GmPHYB2. Soybean PHYAIPHYB shared over70%similarity with Arabidopsis PHYA/PHYB, and over80%similarity with legume PHYA/PHYB in amino acid sequences. In addition, soybean PHYA/PHYB have conserved gene structures and functional domains with phytochromes of other plants.Real-time quantitative RT-PCR (qPCR) detection shows that, there is no obvious expression rhythm for soybean PHYA and PHYB in long day and short day conditions, indicating that the expression of soybean phytochromes may not be regulated by circadain clock.Through ectopic expression analysis, it is found that soybean GmPHYB1plays a similar role as Arabidopsis PHYB does in case of shade avoidance response, flowering time and photomorphogenesis. Overexpression of the soybean GmPHYBl leads to dwarf and compact plant architecture, early flowering under short day conditions and strong inhibition of hypocotyl elongation. In some cases, GmPHYB1functions more powerfully than Arabidopsis PHYB does. In short day conditions, GmPHYBl overexpressing plants flower earlier than AtPHYB overexpressing ones. When the red light intensity ranges between0.25μmol m-2s-1and0.6μmol m-2s-1or blue light intensity ranges between10μmol m-2s-1and25μmol m-2s-1, the inhibition of hypocotyl elongation is more significant in GmPHYBl overexpressing plants than in AtPHYB overexpressing ones. The results indicate that soybean phytochrome might be different from Arabidopsis phytochrome in some aspects.Detection of expression level of the downstream genes in transgenic Arabidopsis plants reveals that in short day conditions overexpression of Arabidopsis PHYB or soybean GmPHYB1in Arabidopsis leads to increasing expression levels of circadian oscillators genes LHY, CCA1and TOC1and flowering gene FT and CO, indicating that GmPHYB1shared the similar mechanisms in flowering regulation with its homologs in Arabidopsis.PHYB (GmPHYB1or AtPHYB) overexpression in Arabidopsis leads to increased number and branches of trichomes, especially on the stem, indicating that PHYB is related to the occurrence of trichomes. So far, there is no literature concerning the relationship between PHYB and the occurrence of trichomes. The hypocotyl of Col-0plants overexpressing GmPHYA1in far-red light becomes longer compared with Col-0plants. And the overexpression of GmPHYA1has no effect on flowering. These mechanisms wait to be uncovered in future.