Study On Molecular Mechanism Of Shade Induced Senescence Regulated By Phytochrome A In Arabidopsis Thaliana

Light is an important environment factor that affects plant growth and development.Plants are highly sensitive to changes of optical signals in the environment and have evolved complex light perception and transduction systems,for example the model plant Arabidopsis Thaliana use phytochrome(phyA-phyE)to perceive changes in red light and far-red light.The ratio of red light and far-red light(R:FR)in shade environment has been reduced,and plants perceive the light signal through phytochrome and then induce series of shade avoidance response(SAR)such as rapid elongation of petioles and hypocotyls,in addition plants also exhibit senescence phenotype under shade.PhyA has a certain inhibitory effect on the shade induced senescence,and phyA mutant showed accelerated senescence phenotype under strong shade,but the specific regulatory mechanism was not clear.Phytohormone ethylene can promote the maturity of the fruits and vegetables and rapid senescence of flowers and leaves,and ethylene signaling pathway regulates the natural and induced senescence process positively.It has been reported that shade could induce the production of ethylene in tobacco plants.In this paper,we found that under shade phyA inhibit the transcriptional and protein levels of EIN3 and the expression of EIN3 target genes,and phyA can regulate shade induced senescence by suppressing ethylene signaling pathway.PIF4/5 are key transcription factors in the regulation of shade avoidance response.We found that phyA can inhibit PIF4/5 protein level and the expression of PIF4/5 target genes,in addition phyA can also suppress the transcriptional activation of ethylene synthesis associated gene ACS8 through PIF4/5,but it seems that PIF4/5 was not involved in the phyA-mediated regulation of shade induced senescence and the expression of downstream genes in ethylene pathway.Changes in iron homeostasis may affect the chlorophyll content in plants.We found that the expression of iron homeostasis related genes such as FR06,FER1,NEET were changed under shade and regulated by phyA.Thus we speculate that phyA may regulate the chlorophyll content under shade by regulating iron homeostasis in plants.