Molecular Mechanism Of The Wood Formation Between Juvenile And Mature Phases In Populus

The wood formed at juvenile and mature phases has disparate physical and chemical characters,resulting in distinct wood property at different life stages.Com-pared with juvenile wood,mature wood has the characteristics of higher wood density,longer xylem cells,thicker secondary cell wall,higher crystalline cellulose content and smaller fibril angle.However,the genetic mechanisms involved in juvenile and mature wood formation has not been elucidated.The Populus plantation trees from a single clone with the same genetic background and and growth conditions allow in-vestigation of the transcriptional programming and regulatory networks during juve-nile wood and mature wood formation.Firstly,we performed tissue anatomy and component analysis on 2 year old(juvenile phase,JP)and 8 year old(mature phase,MP)poplar.The results show that the mature wood is characterized by longer and larger fiber and vessel with higher content of cellulose and hemicelluloses but less lignin compared to the juvenile wood.Secondly,Genome-wild gene expression pro-filing in juvenile and mature wood-forming tissues indicated 4169 genes were signif-icantly differentially expressed between JP and MP.Among them,1982 genes were up-regulated in MP,and 2187 genes were down-regulated in MP.The analysis re-vealed that different transcriptional regulatory networks act in juvenile and mature phases.Among these genes,we found that the expression patterns of genes such as PINs,ABCAs,AUXs which involved in the distribution of auxin and genes such as DIM,BAK1,BSK1,BZR1 which involved in the brassinosteroids biosynthesis/sig-naling pathway has significantly differentially between JP and MP,which may play a critical role in formulating different wood properties between the juvenile wood and the mature wood.Meanwhile,325 transcription factors(TFs)were identified in dif-ferentially expressed genes,including many TFs involved in auxin response and ac-tivity regulation like ARFs,SRSs,Dofs,and MYBs and NACs that regulate cell wall biosynthesis.Furthermore,expression patterns of genes related to cell division,like CDCKs and CYCs,genes related to cell expansion,like XTHs and expansin,genes related to secondary cell wall biosynthesis,like PAL,4CL,C4H,UXS,CSLA were consistent with the physiochemical features in the juvenile and mature wood.In this study,we combined the analysis of the characteristics of juvenlie wood and mature wood,and identified regulatory networks hereby are provided of wood formation at different phrase in Populus,which provides a new perspective for better understandind of wood formation and provides a available genetic resources for im-prove wood property.