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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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