Six new cellulose synthase genes from Eucalyptus are associated with primary and secondary cell wall biosynthesis

Higher plants contain a family of cellulose synthase catalytic subunit (CesA) genes that encode components of an enzyme complex embedded in the cell membrane. Recent studies in several higher plant species have demonstrated that two groups of CesA genes exist, associated with either primary or secondary cell wall deposition. We cloned six full-length CesA cDNAs from Eucalyptus grandis W. Hill ex Maiden (EgCesA1 through 6) and determined their expression patterns in a variety of organs from an adult tree. The six EgCesA genes encode predicted proteins of 978 to 1097 amino acid residues, each of which contains all of the key regions and motifs characteristic of functional CESA proteins. The predicted proteins share limited amino acid identity with each other, ranging from 61 to 70%. In contrast, similar CESA proteins from higher plant species exhibit 81 to 90% identity with the six EgCESAs. Gene expression analysis using quantitative reverse-transcription polymerase chain reaction indicated that transcripts of EgCesA1 to 3 were abundant in tissues enriched with cells laying down secondary cell walls (e.g., xylem), but were weakly expressed in tissues undergoing primary growth (e.g., unfolding leaves). Expression of EgCesA4 and EgCesA5 was upregulated in tissues rich in rapidly dividing cells undergoing primary wall synthesis, whereas EgCesA6 was weakly expressed in all tissues analyzed. These results suggest that Eucalyptus, like other higher plants, expresses two contrasting groups of apparently co-regulated CesAs involved in either primary or secondary cell wall biosynthesis.