Function Of BpAP1 In Betula Platyphylla×Betula Pendula

APETALA1(AP1)is an MADS-box transcription factor,involving in the flowering transition in plants,and has been the focus of much research.In this study,we chose BpAPl overexpression line,BpAPl suppression line and non-transgenic Betula platyphylla × Betula pendula(birch)as materials,analyzed growth and development,flowering,wood property and spatio-temporal expression of BpAP1,meanwhile combined with RNA-Seq and birch genome sequence to predict target genes of BpAP1,discussed relationship between BpAP1 and the target genes.These results provide reference to reveal function of BpAPl in flowering transition and the role of growth and development of birch.(1)Overexpression of BpAP1 caused early-flowering;these lines had an obviously shortened juvenile phase.In BpAP1 overexpression lines,inflorescences emerged successively beginning two months after transplanting.In addition,the length-diameter ratio of fully-developed male and female inflorescences were both significantly less than those of the WT(P<0.01),Ratio of female and male inflorescence is 1:13,significantly lower than WT(2:1).The male inflorescences emerged early,with empty,draped anthers,and pollen was rarely produced,while the female floret structure was not different from WT.The pistils developed normally and could accept pollen,leading to the production of hybrid progeny(T1).PCR analysis of T1 seedlings of 35S::BpAPl transgenic birch revealed that,on average,BpAP1 was present in 52.5%of the progeny,which basically conformed to 1:1 Mendelian inheritance.We demonstrate that BpAP1 can be inherited through sexual reproduction.(2)BpAP1 overexpression lines were significantly "dwarf',and the average height of two-year-old 35S::BpAP1 plants was significantly lower(41.17%)than that of non-transgenic plants.BpAP1 suppression lines have not been flowering yet,45.45%lines were higher than NT,and some BpAP1 suppression lines showed the trunk bending.(3)Analysis of wood properties showed that total lignin content and syringyl lignin of BpAP1 overexpression and suppression lines were all significantly lower than NT,total lignin content of BpAPl overexpression line was lower 12.65%than NT,and total lignin content of BpAP1 suppression line was lower 13.68%than NT;Wooden fiber cell walls of BpAP1 overexpression and suppression lines were all significantly thinner than NT,36.40%and 27.32%thinner than NT respectively.(4)The expression pattern of BpAPl in different tissues of the wild-type plants was analyzed,and results showed that the expression level of BpAPl in female and male inflorescence was significantly higher than that in the other four parts,with 237.50-fold and 314.14-fold higher expression than the average expression levels of this gene in the other plant parts,this illustrated that BpAPl is a floral organ morphological characteristics gene in birch;BpAP1 expression in roots,shoots,leaves,terminal buds of 35S::BpAP1 transgenic line were all significantly higher than WT and 35S::BpAPIRNAi transgenic line,and the expression of BpAP1 in 35S::BpAP1RNAi transgenic line was significantly lower than that in female and male inflorescence of WT and in each parts of 35S::BpAP1 transgenic line.(5)Expression of BpAP1,BpMADS4,BpMADS5,FT,TFL1,BpP1 and LFY in leaves and male inflorescences of BpAPl overexpression plants in different development stages were all much higher than NT and 35S::BpAP1RAAi transgenic lines,expression of these genes was the highest in different stages in male inflorescence except BpAPl and TFL1,and expression peak of most of these genes appeared in 15 June.There is a significant positive correlation between BpAPl and other six genes.(6)RNA-Seq showed us that there were 8302 and 7813 differential expression unigenes in 35S::BpAPl transgenic line and 35S::BpAP1RNAi transgenic line respectively;over-expressed and suppressed of BpAPl effected diterpenoid biosynthesis and lignin biosynthesis,and caused expression of many flowering related genes changed.Compared with NT,expression of BpAP1 in 35S::BpAP1 transgenic line was significantly up-regulated,expression of FT?ELF4 and FKF1 were significantly up-regulated,while flower repressors including FLC were variously down-regulated,and most of expression of these genes in 35S::BpAP1RNAi transgenic line were opposite with 35S::BpAP1 transgenic line,and there was no significant differential expression in least of them.Combined with transcriptome and birch genome sequence to predict target genes of BpAP1,and obtained 166 target genes,including Protein kinase,Cytochrome P450,Zinc finger-containing,MADS-box transcription factor,Plant peroxidase and Protein of unknown function,and so on.BpP1 and BpAP3 are the two MADS-box transcription factor target genes of BpAPl.There is a significant positive correlation between BpAPl and BpPI,and positive correlation between BpAPl and BpAP3.