Functional Analyses Of Maize PHYB1 In Arabidopsis Thaliana

As an important environmental factor,light affects many aspects of plant development,such as flowering time,seed germination,and stress resistance.Plants use several classes of photoreceptors to perceive the light signals in the ambient environment.Among the photoreceptors,phytochromes,which sense red and far-red light signals,are best studied so far.Previous studies have shown that changing the tyrosine?Y?at position 104 and 361 of Arabidopsis phyB to phenylalanine?F?can enhance its activity.The maize genome contains two genes encoding phytochromes,phytochorme B1?PHYB1?and phytochrome B2?PHYB2?.To investigate the function of maize phytochrome B1,we constructed three binary vectors:wild type ZmPHYB1^WT,ZmPHYB1^Y98F?mimicking Y104F of Arabidopsis phyB?and ZmPHYB1^Y359F?mimicking Y361F of Arabidopsis phyB?,and transformed them into Arabidopsis phyB-9 loss-of-function mutant.Phenotypic and functional analyses of the transgenic lines were performed.The main results are as follows:1.Multiple independent homozygous transgenic lines were obtained through Basta resistance selection.2.Under white light?WL?and red light?Rc?treatments,the hypocotyls of all transgenic lines were significantly shorter than the phyB-9 mutant,and ZmPHYB1^Y98F and ZmPHYB1^Y359F359F transgenic lines had shorter hypocotyl than the wild type ZmPHYB1^WT transgenic lines;leaf petioles of the transgenic lines were also shorter than the phyB-9 mutant under long day conditions3.All three forms of ZmPHYB1s-YFP in the transgenic lines can enter the nucleus under red light treatment,forming green speckles;4.The transgenic lines flowered later than phyB-9,and the number of rosette leaves increased.Besides,the ZmPHYB1^Y98F and ZmPHYB1^Y359F transgenic lines flowered even more later than the wild type ZmPHYB1^WT transgenic lines;5.All three forms of ZmPHYB1 interacted with AtPIF1/3/4/5 in the nucleus;6.The expression levels of shade-responsed genes ATHB2,IAA29,PIL1,HFR1 and the auxin responsed genes YUC5,YUC8,and YUC9 were altered in the there transgenic lines.In summary,the above results suggest that maize PHYB1 gene can largely complement the Arabidopsis phyB-9 mutant phenotypes,including hypocotyl elongation,petiole length and flowering time,but could not effectively restore chlorophyll biosynthesis.The Y98F and Y359F amino acid substitutions can enhance the activity of ZmPHYB1.At the molecular level,ZmPHYB1 can physically interact with the Arabidopsis PIFs proteins and induce the expression of downstream shade avoidance response and auxin biosynthesis related genes.