Molecular Mechanism Of Far-red Photoreceptor PhyA Promoting Plant Photomorphogenesis By Inhibiting Brassinolide Signaling

Light is an important environmental factor for plant growth and development,and it provides energy and signal sources for plant growth and development.In order to adapt to the environment,plants have evolved multiple photoreceptors to sense light signals in the environment.Among them,phytochromes(phys)are the main red and far-red photoreceptors,including five members of phyA-phyE,of which phyA is a farred photoreceptor and phyB-E are red photoreceptors.They play an important role in the process of phoromorphogenesis,shade avoidance,anthocyanin synthesis and flowering.Phytochromes exist in the inactive Pr form in the dark,are converted to Pfr form after being irradiated by red light,and enter the nucleus to function.On the one hand,phytochromes in the nucleus interact with COP1/SPA complex,a key negative regulator of photomorphogenesis,inhibiting its activity and promoting the protein accumulation of multiple positive regulators of photomorphogenesis;on the other hand,phytochromes can interact with PIFs that negatively regulate photomorphogenesis to promote the phosphorylation and degradation of PIFs,thereby promoting photomorphogenesis.Brassinosteroid(BR)is a class of steroid hormones that regulate the growth,development and gene expression of animals and plants.Brassinosteroid was first extracted from rape pollen,and later found in the growth tissues of most higher plants,with the highest content in pollen,seeds and fruits.As an important plant hormone,BR is mainly involved in the regulation of cell elongation,cell division,fertility,seed germination and plant photomorphogenesis.BR signal transduction starts from the binding of BR to the membrane receptor BRI1,and the activated BRI1 recruits the coreceptor kinase BAK1,which inactivates the negative regulator BIN2 through a series of cascade reactions.Thus,BES1/BZR1,the main transcription factor of the BR signaling pathway,cannot be phosphorylated by BIN2.Moreover,BES1/BZR1 is dephosphorylated by PP2 A,so that BES1/BZR1 is in a non-phosphorylated active state,and accumulates in large amounts in the nucleus to regulate the expression of downstream genes.Previous studies have found that red light-activated phyB can directly interact with the non-phosphorylated form of BES1,inhibiting its DNA-binding activity,inhibiting BR signaling and promoting photomorphogenesis.In addition,blue light-activated CRY1 can interact with the non-phosphorylated form of BES1,inhibiting its DNA binding ability;CRY1 can also interact with BIN2 and BZR1,and promote the interaction between BIN2 and BZR1,thereby inhibiting the expression of BRresponsive genes Expresses and promotes photomorphogenesis.The UV-B photoreceptor UVR8 can also interact with BES1 and BIM1 to regulate BR signaling.However,whether the phyA-mediated far-red light signaling pathway regulates BR signaling is largely unclear.In this study,through biochemical,molecular,genetic and other technical means,it was found that phyA can interact with BIN2 protein in a far-red light-dependent manner.Moreover,phyA can promote the interaction between BIN2 and BES1.In addition,phyA can promote the accumulation of BIN2 substrate BES1 in a phosphorylated form,inhibit the expression of BR-responsive genes,and promote photomorphogenesis in Arabidopsis seedlings under far-red light.Genetic studies of hypocotyl length and anthocyanin content phenotype revealed that BIN2 plays a partial role downstream of PHYA to regulate plant photomorphogenesis under far-red light.This study further improves the molecular mechanism of the interaction between exogenous light signals and endogenous hormone signals,so that plants can better adapt to the changing external environment,and provides a new research perspective for the study of the molecular mechanism of plant growth and development.The practical application and agricultural production have laid a theoretical foundation.