Chalcone synthases (CHS, EC 2.3.1.74) are key enzymes that catalyze the first committed step in flavonoid biosynthesis. In this study, we isolated a chalcone synthase, named NtCHS6, from Nicotiana tabacum.  This synthase shared high homology with the NSCHSL (Y14507) gene and contained most of the conserved active sites that are in CHS proteins.  The phylogenetic analysis suggested that NtCHS6 protein shared a large genetic distance with other Solanaceae CHS proteins and was the most closely-related to an uncharacterized CHS from Solanum lycopersicum.  The expression analysis indicated
that NtCHS6 was abundantly expressed in leaves, especially in mature leaves.  By scrutinizing its upstream promoter sequences, multiple cis-regulatory elements involved in light and drought responsive were detected.  Furthermore, NtCHS6 expression decreased significantly under dark treatment and increased significantly under drought stress.  Our results suggested that NtCHS6 expression exhibited both light responsiveness and drought responsiveness, and might play important roles in ultraviolet protection and drought tolerance.

Calcium-dependent protein kinases (CDPKs, EC 2.7.1.37) comprise a large family of Ser/Thr kinases in plants and play an important role in plant Ca2+ signal transduction. A full-length CDPK gene, NtCDPK12 (GenBank accession number GQ337420), was isolated from common tobacco (Nicotiana tabacum) leaves by rapid amplification of cDNA ends (RACE). The NtCDPK12 cDNA is 1 816 bp length and contains an open reading frame (ORF) of 1 461 bp encoding 486 amino acids. Sequence alignments indicated that NtCDPK12 contains all conserved regions found in CDPKs and shows a high level of sequence similarity to many other plant CDPKs. The results of real-time quantitative reverse transcription-PCR (qRTPCR) showed that NtCDPK12 was highly expressed in stems and increased in roots treated with high-salt or subjected to drought stress, which indicates that NtCDPK12 was induced by high-salt and drought stresses.