NAC TFs, such as PpNAC1 and PpNAC30 from P. pinaster, PgNAC7 from
white spruce or PtrWND2B and PtrWND6B from P. trichocarpa, could act at the
first level of the transcriptional regulatory network involved in wood formation,
while Myb TFs could function at the second level, along with other MYB and NAC
TFs (Fig. 4). For example, PtrMyb20 and PtrMyb3 from poplar and EgMyb2 and
Pt/PpMyb4 from eucalyptus and pine, respectively, are functional orthologs of
NAC master switch
MYB master
switch
Lignin-specific MYBs
Lignin
Cellulose Hemicellose/ Xylan
Secondary Cell Wall Biosynthesis
TFs activating three SCW
biosynthetic pathways
PpNAC1
PpMyb4
PpMyb8
Pt/PgMyb4
PpNAC30
PgNAC–7
PgNAC8
PgMyb8
EgWND1
EgMyb2
PtrWND2
PtrWND6
PtrMyb26
PtrMyb28
PtrMyb90
PpMyb1
PgCesA, PgXTH
Pg/PpCAD, Pg4CL
PpCCoAOMT,
PpC3H, PpHCT
PpCesA4
PtrMyb18
PtrMyb74
PtrMyb75
PtrNAC150
PtrMyb20
PtrMyb3
PtrWND1
PtrWND3
PtrWND4
PtrWND5
Fig. 4 Proposed transcriptional network controlling secondary cell wall biosynthesis in trees. NAC
and Myb TFs from P. pinaster, P. glauca and P. trichocarpa are shown. Continuous lines indicate
that the interactions have been functionally demonstrated
NAC Transcription Factors in Woody Plants
213