Abstract:
The differentiation of cork (phellem) cells from the
phellogen (cork cambium) is a secondary growth process
observed in the cork oak tree conferring a unique ability to
produce a thick layer of cork. At present, the molecular
regulators of phellem differentiation are unknown. The previously
documented involvement of microRNAs (miRNAs) in
the regulation of developmental processes, including secondary
growth, motivated the search for these regulators in cork
oak tissues.We performed deep sequencing of the small RNA
fraction obtained from cork oak leaves and differentiating
phellem. RNA sequences with lengths of 19–25 nt derived
from the two libraries were analysed, leading to the identification
of 41 families of conservedmiRNAs, of which the most
abundant were miR167, miR165/166, miR396 and miR159. Thirty novel miRNA candidates were also unveiled, 11 of
which were unique to leaves and 13 to phellem. Northern blot
detection of a set of conserved and novel miRNAs confirmed
their differential expression profile. Prediction and analysis of
putative miRNA target genes provided clues regarding processes
taking place in leaf and phellem tissues, but further
experimental work will be needed for functional characterization.
In conclusion, we here provide a first characterization of
the miRNA population in a Fagacea species, and the comparative
analysis of miRNA expression in leaf and phellem
libraries represents an important step to uncovering specific
regulatory networks controlling phellem differentiation.
