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of rehydration involved up-regulation of as many as 259 genes whereas 13 genes showed rehydration
specifi c down-regulation. Among the 29 genes up-regulated during rehydration, eight genes were for
transcriptional regulators. Six of these belonged to transcriptional repressor family and the rest two
genes were
ancrpB
and ORF
alr0618
. Studies conducted on the gene disruptant mutants of
ancrpB
and
alr0618
conclusively showed that the former gene product AnCrpB is required for recovery of
photosynthesis during late rehydration events and the latter gene product (Alr0618) is related to
inorganic carbon uptake in particular. The cAMP-binding motif is absent in Alr0618 and so it does
not bind to cAMP.
The contribution of EPS to desiccation tolerance in
Anabaena
sp. strain PCC 7120 has been further
confi rmed by the identifi cation of
sigJ
gene (a group 3 sigma factor gene) that regulates synthesis of
EPS. The expression of
sigJ
in terrestrial
Nostoc
HK-01 was signifi cantly induced during mid-phase of
desiccation.
Anabaena
sp. strain PCC 7120 is a freshwater strain and can not tolerate desiccation but
a transformant of
Anabaena
(HE 0277) overexpressing the
alr0277
gene for
sigJ
acquired desiccation
tolerance associated with 3.2 fold higher production of EPS. This has been further confi rmed by
oligonucleotide microarray. Alongwith
sigJ
, the expression of 112 genes was up-regulated and the
expression of 42 genes was down-regulated in the HE 0277 cells during desiccation. Among the
up-regulated genes more than 5% of them belonged to cell envelope genes and the other genes are
for photosynthesis, respiration, transcription and regulatory functions (Yoshimura
et al
. 2007).
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