title: Ptr-miR397a is a negative regulator of laccase genes affecting lignin content in Populus trichocarpa.
abstract: Laccases, as early as 1959, were proposed to catalyze the oxidative polymerization of monolignols. Genetic evidence in support of this hypothesis has been elusive due to functional redundancy of laccase genes. An Arabidopsis double mutant demonstrated the involvement of laccases in lignin biosynthesis. We previously identified a subset of laccase genes to be targets of a microRNA (miRNA) ptr-miR397a in Populus trichocarpa. To elucidate the roles of ptr-miR397a and its targets, we characterized the laccase gene family and identified 49 laccase gene models, of which 29 were predicted to be targets of ptr-miR397a. We overexpressed Ptr-MIR397a in transgenic P. trichocarpa. In each of all nine transgenic lines tested, 17 PtrLACs were down-regulated as analyzed by RNA-seq. Transgenic lines with severe reduction in the expression of these laccase genes resulted in an ∼40% decrease in the total laccase activity. Overexpression of Ptr-MIR397a in these transgenic lines also reduced lignin content, whereas levels of all monolignol biosynthetic gene transcripts remained unchanged. A hierarchical genetic regulatory network (GRN) built by a bottom-up graphic Gaussian model algorithm provides additional support for a role of ptr-miR397a as a negative regulator of laccases for lignin biosynthesis. Full transcriptome-based differential gene expression in the overexpressed transgenics and protein domain analyses implicate previously unidentified transcription factors and their targets in an extended hierarchical GRN including ptr-miR397a and laccases that coregulate lignin biosynthesis in wood formation. Ptr-miR397a, laccases, and other regulatory components of this network may provide additional strategies for genetic manipulation of lignin content.
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100193, China.
authors.forename: Shanfa
authors.initials: S
authors.lastname: Lu
authors.forename: Quanzi
authors.initials: Q
authors.lastname: Li
authors.forename: Hairong
authors.initials: H
authors.lastname: Wei
authors.forename: Mao-Ju
authors.initials: MJ
authors.lastname: Chang
authors.forename: Sermsawat
authors.initials: S
authors.lastname: Tunlaya-Anukit
authors.forename: Hoon
authors.initials: H
authors.lastname: Kim
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Jingyuan
authors.initials: J
authors.lastname: Song
authors.forename: Ying-Hsuan
authors.initials: YH
authors.lastname: Sun
authors.forename: Lichai
authors.initials: L
authors.lastname: Yuan
authors.forename: Ting-Feng
authors.initials: TF
authors.lastname: Yeh
authors.forename: Ilona
authors.initials: I
authors.lastname: Peszlen
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Sederoff
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Chiang
mesh_terms: D001483:Base Sequence; D015536:Down-Regulation / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D053263:Gene Regulatory Networks; D017343:Genes, Plant; D042845:Laccase / Q000037:antagonists & inhibitors / Q000235:genetics*; D008031:Lignin / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D032107:Populus / Q000201:enzymology* / Q000235:genetics*; D018749:RNA, Plant / Q000235:genetics* / Q000378:metabolism*
chemical_list: D035683:MicroRNAs; D010940:Plant Proteins; D018749:RNA, Plant; D008031:Lignin; D042845:Laccase