Effects And Mechanisms Of Overexpressing Phy A On Peanut Plant Architecture

Plant architecture is an important trait which affects crops yield and adaptability to the environment and is subjected to strict genetic control.Plant architecture includes plant height,leaf type,tiller number,tiller angle,inflorescence,etc.Plant height is an important trait that affects plant architecture and reflects plant growth.The inflorescence is the arrangement of flowers and flowering pattern in the floral branch.Studies have shown that the length of the inflorescence axis is closely related to the yield of soybean.And the longer the inflorescence axis,the later the first flowering time of the plant,the longer the flowering period,and the late flower phenotype appeared.There are a variety of factors that affect plant architecture.In addition to the environmental factors,plant hormones,cell cycle regulatory factors,and key genes for cell wall synthesis all play key roles in regulation of plant architecture.phytochrome A is photoreceptor for far-red light.Studies showed that phyA overexpression lines exhibited dwarf phenotype in Arabidopsis.Heterologous expression of oat phyA in tobacco led to a decrease in bioactive gibberellin（GAs）and plant dwarfism.Exogenous GA application suppressed this dwarf phenotype.The elongation of coleoptile in phyA overexpression lines of rice was inhibited,and the mature transgenic rice plants significantly decreased in plant height,internode length,etc.,and the number of panicle per plant increased.It could be speculated that phyA plays a key role in regulation of plant architecture,however,its regulation mechanism has not been deeply studied in peanut.AhphyA overexpressing lines（OEphyA）in peanut with stable phenotype were obtained in our previous studies.The transgenic lines of OEphyA had the characteristics of dwarfism.In this study,OEphyA was used as materials to analyze plant height,branching,inflorescence length and other traits.The effects of different light qualities on hypocotyl and root growth of OEphyA were analyzed.The regulation mechanisms of phyA on plant height and inflorescence elongation were investigated by digital gene expression profiling,hormone content determination,and exogenous hormone treatment.The main results of this study are as follows:1.Effects of different light on hypocotyl and root growth:Under the four conditions of red light,far red light,darkness and white light,after 6,9,12 d,the hypocotyl and root length OEphyA and LH14 were measured.The results showed that the length of OEphyA hypocotyl was significantly shorter than that of LH14 in red light,far red light,and white light.The length of OEphyA root was significantly longger than that of LH14 in red light,far red light,and dark conditions,while there was no difference in white light conditions.2.Phenotypic analysis of OEphyA:At the mature stage,the main stem height and lateral branch length of OEphyA were significantly shorter than that of LH14.The first flower of OEphyA flowered 6 d later than that of LH14.The chlorophyll a,b,and carotenoid contents of OEphyA were significantly lower than those of LH14 in the unexpanded young leaves.The chlorophyll a and b content of mature leaves of OEphyA main stem were significantly higher than those of LH14,indicating that phyA overexpression could promote chlorophyll accumulation in mature leaves.3.Analysis of the digital gene expression profiles in aerial-grown pegs:phyA overexpression in peanuts cause a series of changes in gene expression of genes related to light signals,hormones,cell wall formation and embryonic development.It was showed that he expression of AhphyA in OEphyA was up-regulated by 1.32 and4.24 times in the expression profile and qRT-PCR,respectively.The expression levels of auxin-related genes,ABA signal-related genes,and ethylene signal transduction-related genes in OEphyA were decreased,while the expression levels of GA signal-related genes were increased.In addition,the expression of gibberellin 20oxidase 2-like was significantly down-regulated.These GA-related gene changes may eventually lead to decreased GA content,resulting in a dwarf phenotype of OEphyA.4.Analysis of the digital gene expression profiling and hormone content in peanut leaves:The analysis of the digital gene expression profile of peanut seedling leaves showed that the expression of genes related to gibberellin biosynthesis was down-regulated while the expressions of GA degradation related genes were up-regulated.These results suggested that the dwarf phenotype of OEphyA may be related to the decreased GA content.Genes promoting flowering were down-regulated,and OEphyA had the late flowering phenotype.Hormone measurement results showed that compared with the control LH14,the IAA content in the OEphyA did not change significantly,while the GA content was significantly reduced.We further speculated that the dwarf phenotype of OEphyA may be caused by the decrease of GA content.5.Effcts of GA and GA inhibitor on peanut plants:the 14 d LH14 and OEphyA seedlings were treated with GA and GA inhibitor.For the untreated control,the main stem height of OEphyA was significantly shorter than that of LH14.After GA₃treatment,there was no significant difference between the height of the main stem of OEphyA and LH14,indicating that GA₃ treatment can recover the growth of OEphyA main stem.After GA inhibitor treatment,the height of LH14 main stem was similar to that of OEphyA.These results further confirmed that the dwarf phenotype of OEphyA was caused by the reduced GA content.6.Study on the elongation of OEphyA inflorescence axis:Compared with LH14,the inflorescence axis of OEphyA was significantly elongated,and the numbers of pegs and pods of OEphyA were incresased.In order to explore the molecular mechanism of OEphyA inflorescence axis elongation,LH14 and OEphyA inflorescence axis were used for gene expression profiling and hormone content determination.The results showed that the content of GAs and IAA in OEphyA inflorescence axis increased significantly.Therefore,we speculated that the elongation of the OEphyA inflorescence axis may be related to GAs and auxin.