Abstract:
Lignocellulosic biomass from fast-growing plantation
trees is composed of carbohydrate-rich materials deposited
into plant cell walls in a coordinated manner during
wood formation. The diversity and evolution of the transcriptional
networks regulating this process have not been
studied extensively.We investigated patterns of species-level
nucleotide diversity in the promoters of cellulose synthase
(CesA) genes from different Eucalyptus tree species and
assessed the possible roles of DNA sequence polymorphism
in the gain or loss of cis-elements harboured within the
promoters. Promoter regions of three primary and three
secondary cell wall-associated CesA genes were isolated
from 13 Eucalyptus species and were analysed for nucleotide
and cis-element diversity. Species-level nucleotide diversity (π) ranged from 0.014 to 0.068, and different CesA promoters
exhibited distinct patterns of sequence conservation.
A set of 22 putative cis-elements were mapped to the CesA
promoters using in silico methods. Forty-two percent of the
mapped cis-element occurrences contained singleton polymorphisms
which resulted in either gain or loss of a ciselement
in a particular Eucalyptus species. The promoters of
Eucalyptus CesA genes contained regions that are highly
conserved at the species (Eucalyptus) and genus (with
Arabidopsis and Populus) level, suggesting the presence of
regulatory modules imposing functional constraint on such
regions. Nucleotide polymorphisms in the CesA promoters
more frequently created new cis-element occurrences than
disrupted existing cis-element occurrences, a process which
may be important for the maintenance and evolution of
cellulose gene regulation in plants.
