ANALYSIS OF XYLEM FORMATION IN PINE BY CDNA SEQUENCING

Secondary xylem (wood) formation is likely to involve some genes expre ssed rarely or not at all in herbaceous plants. Moreover, environmenta l and developmental stimuli influence secondary xylem differentiation, producing morphological and chemical changes in wood. To increase our understanding of xylem formation, and to provide material for compara tive analysis of gymnosperm and angiosperm sequences, ESTs were obtain ed from immature xylem of loblolly pine (Pinus taeda L.), A total of 1 ,097 single-pass sequences were obtained from 5' ends of cDNAs made fr om gravistimulated tissue from bent trees, Cluster analysis detected 1 07 groups of similar sequences, ranging in size from 2 to 20 sequences , A total of 361 sequences fell into these groups, whereas 736 sequenc es were unique. About 55% of the pine EST sequences show similarity to previously described sequences in public databases. About 10% of the recognized genes encode factors involved in cell wall formation, Seque nces similar to cell wall proteins, most known lignin biosynthetic enz ymes, and several enzymes of carbohydrate metabolism were found. A num ber of putative regulatory proteins also are represented. Expression p atterns of several of these genes were studied in various tissues and organs of pine, Sequencing novel genes expressed during xylem formatio n will provide a powerful means of identifying mechanisms controlling this important differentiation pathway.