ABSTRACT
KEY MESSAGE: The evolutionary origin of the phytochrome genes in soybean was analyzed. The expression profiles of PHYA paralogs were characterized. The heterologous expression of GmPHYA1 in Arabidopsis resulted in longer hypocotyls. The phytochromes (PHY) are a small family of red/far-red light photoreceptors which regulate a number of important developmental responses in plants. So far, the members of the PHY gene family in soybean (Glycine max) remain unclear and an understanding of each member's physiological functions is limited. Our present in silico analysis revealed that the soybean genome harbors four PHYA, two PHYB and two PHYE, totally four pairs of eight PHY loci. The phylogenetic analysis suggested that the four PHY paralogous pairs originated from the latest round of genome duplication (~13 million years ago) and the four copies of PHYA were remnants of the two rounds of genome duplication (~58 and ~13 million years ago). A possible evolutionary history of PHYA homologs in the three legume species (soybean, Medicago truncatula, and Lotus japonicus) was proposed and the fate of duplicate soybean PHYA genes following polyploidization was discussed. The expression profiles of a soybean PHYA paralogous pair (GmPHYA1 and GmPHYA2) showed that the transcript abundance was highest in the aerial organs of young plants. The physiological role of GmPHYA1 was explored by observing the de-etiolation phenotype of transgenic Arabidopsis plants constitutively expressing GmPHYA1. The GmPHYA1 protein interfered with the function of endogenous PHYA with respect to de-etiolation in a dominant negative manner when exogenously expressed in Arabidopsis. The elucidation of the PHY gene family members in soybean provide us with a general description and understanding of the photoreceptor gene family in this important crop plant.
Subject(s)
Arabidopsis/genetics , Genes, Dominant/genetics , Genes, Plant/genetics , Glycine max/genetics , Multigene Family , Phytochrome A/genetics , Transgenes/genetics , Arabidopsis/radiation effects , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Chromosomes, Plant/genetics , Cotyledon/genetics , Cotyledon/growth & development , Cotyledon/radiation effects , Gene Expression Profiling , Gene Expression Regulation, Plant/radiation effects , Hypocotyl/genetics , Hypocotyl/growth & development , Hypocotyl/radiation effects , Light , Phylogeny , Phytochrome A/metabolism , Plants, Genetically Modified , RNA, Messenger/genetics , RNA, Messenger/metabolism , Sequence Homology, Nucleic Acid , Glycine max/radiation effectsABSTRACT
Phytochromes sense red/far-red light and trigger a cascade of physiological responses in plant. Here, a phytochrome B homolog, GmPHYB1, was amplified from the soybean genome, and its expression profiles were obtained for various parts of the plant and at various developmental stages. The gene was ectopically expressed in Arabidopsis thaliana, driven by CaMV 35S promoter, to study the physiological functions of the gene product. The overexpressors of GmPHYB1 behaved similarly to those of AtPHYB, but with some subtle differences with respect to the acceleration of flowering under short day conditions and the growth of the hypocotyl under certain light fluence rate. The results suggested that this soybean PHYB homolog was well conserved both at the level of sequence and physiological function.
