Cloning and expressional analyses of a cinnamoyl CoA reductase cDNA from rice seedlings

Abstract

Cinnamoyl CoA reductase (CCR: EC 1.2.1.44), the entry-point enzyme of the lignin specific biosynthetic pathway, catalyzes the conversion of cinnamoyl CoA esters to their corresponding cinnamaldehydes. Multiple sequence alignment showed that the deduced polypeptide shared 70% similarity and 30% sequence identity at the amino acid level with definedCCR genes from other plant species and they all contain the common signature sequences thought to be the catalytic site as well as the putative NADP binding domain. Using a conservedOsCCR cDNA fragment as the probe for library screening, we isolated the genomic DNA that covered the whole coding region ofOsCCR with total length of 3045 bp including 4 introns and 5 exons. The open reading frame for ourOsCCR gene contains 337 amino acids. Northern blot indicated thatOsCCR was expressed in different organs with the highest level found in stems.In situ hybridization results showed thatOsCCR mRNA was localized mainly along the vascular bundles in stems and leaves, and also in lateral roots that was differentiating from the tillering node. We conclude that the vascular-localized expression ofOsCCR gene may suggest its possible involvement in lignin biosynthesis. Cloning and characterization ofOsCCR will help to clarify how lignifications in plants are regulated and will provide a physical basis for creating genetically engineered rice plants with optimal lignin contents.