Using the
mRNA differential display combined with 5' rapid amplification of
cDNA ends (RACE) technique, an early
nodulin-like
protein gene (BcBCP1) (accession no. AY243047.1) was isolated from drought-treated Boea crassifolia leaves. The full-length
cDNA of BcBCP1 consists of 844 bp
nucleotides and has an open reading frame of 606 bp, encoding a putative
polypeptide of 201
amino acids with a predicted molecular mass of 22 kDa and a pI of 5.13. The putative
protein precursor contains four sequence domains, including a 27
amino acid hydrophobic N-terminal transit
peptide, a 100
amino acid phytocyanin-homologous globular domain, a 51
amino acid hydroxyproline-rich cell wall structural protein domain, and a 22
amino acid hydrophobic extension domain. Sequence alignment defined the encoded
protein as an early
nodulin-like
protein, and the absence of key
ligands implies that it is unlikely to bind
copper. BcBCP1 expression was strongly induced by
dehydration, salinity and
abscisic acid (ABA), slightly induced by moderate heat shock, and weakly inhibited by low temperature, methyl
jasmonic acid (MeJA), and a low concentration of
salicylic acid (SA). Overexpression of BcBCP1 in tobacco under the control of CaMV 35S promoter enhanced tolerance to osmotic stress, as indicated by the less impaired growth, less damaged membrane integrity and lower lipid peroxidation levels after osmotic stress. Transgenic tobacco lines overexpressing BcBCP1 showed higher photosynthetic rates, higher
antioxidant enzyme activities and higher cytosyl ascorbic
peroxidase transcription levels than non-transgenic tobacco plants, both under normal conditions and under osmotic stress.