Role of Plant Laccases in Lignin Polymerization - Botanical Research - page 159

ratio of quercetin rhamnoside monomers to dimers, when compared to wild-
type seeds ( Pourcel et al.,2005 ).
There might be also some role for TT10 in primary root development as
mutant roots seem to be significantly shorter than wild-type roots when
grown in vitro ( Liang et al., 2006 ). On the other hand, the root hair density
and the number of inflorescence stems were higher in tt10 than in WT ( Buer
and Djordjevic, 2009 ). All these phenotypes need further confirmation using
several tt10 alleles.
Public microarray data (Genevestigator server, https://genevestigator.
com ) show that the TT10 gene is expressed strongly in siliques, moderately
in flowers and weakly in roots, but is undetected in seedlings, leaves, and
inflorescence stems ( Turlapati et al., 2011 ). Several reports using RT-PCR or
RT-qPCR confirm silique and flower expression ( Cai et al., 2006; Kleindt
et al., 2010; McCaig et al., 2005; Pourcel et al., 2005; Turlapati et al., 2011 ),
but some also detect TT10 mRNA in seedlings, stems ( Pourcel et al., 2005 ),
and leaves ( McCaig et al., 2005; Turlapati et al., 2011 ) but not in roots
( Pourcel et al., 2005 ).
Histochemical analysis of TT10 promoter (pTT10) activity was performed
in several studies using arabidopsis transformants expressing promoter
fusions with the uidA gene that encodes the GUS reporter protein. At the
seed level, Pourcel et al. (2005) showed that pTT10 is active not only in the
tannin-producing and flavonol-producing cells of the inner and outer integu-
ments, respectively (colocalization with the flavonoid substrates), but also in
early aborted seeds. Promoter activity was also detected in funiculus, replum,
and transmitting tissue of the silique ( Pourcel et al., 2005; Turlapati et al.,
2011 ), and in root, leaf, and stem vessels ( Turlapati et al., 2011 ). On the other
hand, Liang et al. (2006) did not detect any activity in roots and leaves.
Interestingly, the TT10 promoter construct studied by Liang et al. (2006) was
also shown to be active in the seed coat of canola (Brassica napus), but
activity was restricted to outer integument ( El-Mezawy et al., 2009 ).
Discrepancies between laboratories in the results concerning TT10 gene
expression and promoter activity might be explained by different environ-
mental conditions used for plant growth or PCR conditions and various
promoter fragments and vectors used in the GUS gene reporter studies.
Indeed, there is experimental evidence showing that the TT10 developmental
spatiotemporal pattern of gene expression can be modulated by external
stimuli such as drought stress ( Turlapati et al., 2011 ) or copper nutrition
( Abdel-Ghany and Pilon, 2008 ).
Candidate transcription factors (TFs) regulating TT10 expression still wait
to be discovered. As explained above, the TT10 laccases was demonstrated
to use flavonoids as in vivo substrates ( Pourcel et al., 2005 ). This activity is