Poplar PdC3H17 and PdC3H18 are direct targets of PdMYB3 and PdMYB21, and positively regulate secondary wall formation in Arabidopsis and poplar

Abstract

SummaryWood biomass is mainly made of secondary cell walls, whose formation is controlled by a multilevel network. The tandem CCCH zinc finger (TZF) proteins involved in plant secondary wall formation are poorly understood.Two TZF genes, PdC3H17 and PdC3H18, were isolated from Populus deltoides and functionally characterized in Escherichia coli, tobacco, Arabidopsis and poplar.PdC3H17 and PdC3H18 are predominantly expressed in cells of developing wood, and the proteins they encode are targeted to cytoplasmic foci. Transcriptional activation assays showed that PdMYB2/3/20/21 individually activated the PdC3H17 and PdC3H18 promoters, but PdMYB3/21 were most significant. Electrophoretic mobility shift assays revealed that PdMYB3/21 bound directly to the PdC3H17/18 promoters. Overexpression of PdC3H17/18 in poplar increased secondary xylem width and secondary wall thickening in stems, whereas dominant repressors of them had the opposite effects on these traits. Similar alteration in secondary wall thickening was observed in their transgenic Arabidopsis plants. qRT-PCR results showed that PdC3H17/18 regulated the expression of cellulose, xylan and lignin biosynthetic genes, and several wood-associated MYB genes.These results demonstrate that PdC3H17 and PdC3H18 are the targets of PdMYB3 and PdMYB21 and are an additional two components in the regulatory network of secondary xylem formation in poplar.

Dual regulation of xylem formation by an auxin‐mediated PaC3H17‐PaMYB199 module in Populus

“…3e). S3; Chai et al, 2014a). These results suggested PaMYB199 represses cambium division and SCW deposition, which would be opposite to the role of PaC3H17 in these two processes (Fig.…”

“…Representative control (the plants transformed with empty vector), PaC3H17 overexpression, and dominant repressor lines (Populus deltoides 9 Populus euramericana cv nanlin'895' background) were described in our previous study (Chai et al, 2014a). Transgenic lines were acclimatized in a mist chamber for 20 d and then transferred to a glasshouse for 4 months in a fully randomized experimental design for phenotypic analysis.…”

“…A 359 bp fragment from the exons of PaMYB199 was inserted into the pUCCRNAi vector in an inverted repeat orientation (primers in Supporting Information Table S1). The PaC3H17DR transgenic poplars containing the PaC3H17 coding region in frame with the EAR-motif repression domain (SRDX) were described previously (Chai et al, 2014a). The 35S:PaMYB199-GFP, 35S:FLAG-PaC3H17 and PaMYB199 RNAi constructs were individually introduced into '84K', and PaMYB199 RNAi into PaC3H17DR plants by Agrobacterium (EHA105)-mediated transformation according to the protocol adopted by our lab (Chai et al, 2014a).…”

“…AtCYCD3 (CYCLIN D3, the orthologue of PaCYCD3) regulates cambial cell proliferation and secondary growth (Collins et al, 2015). 2; Chai et al, 2014a). AtIRX10 (the orthologue of PaIRX10) and AtIRX15-L (the orthologue of PaIRX15L-1/2) are involved in xylose and glucuronoxylan biosynthesis, respectively, during SCW formation (Brown et al, 2009;Wu et al, 2009;Jensen et al, 2011;Urbanowicz et al, 2014).…”

Breeding maize for silage and biofuel production, an illustration of a step forward with the genome sequence

“…Moreover, the over-expression of the two PdC3H17 and PdC3H18 poplar ortholog genes increased secondary xylem width and secondary wall thickening in stems, while their repression had reverse effects. The PdC3H17/18 genes were shown to regulate the expression of cellulose, xylan and lignin biosynthesis genes, and also several related MYB genes [145]. The two AtC3H14 colocalizing maize orthologs were however located at the downstream part of QTL support intervals.…”