Cottoning onto how plants make cellulose

 One of the most abundant materials on Earth also happens to be one of the most enigmatic. Cellulose, a large polymer consisting of numerous sugar molecules linked together, is found in all plant cell walls. It makes trees stand tall, puts the fiber in fruits and vegetables, and gives cotton its puffy boll. Yet the steps plants use to make cellulose have eluded researchers for years, prompting many to turn their attention to other questions.

 Now, a new finding may revive interest in this ubiquitous molecule.

 Scientists at Calgene in Davis, Calif., and the Hebrew University in Jerusalem have identified three plant genes -- one in rice and two in cotton -- each of which may code for cellulose synthase, an enzyme that assembles sugar molecules into cellulose.

 No plant cellulose synthase has yet been isolated, so the researchers sought plant genes that resemble genes known to code for that enzyme in bacteria, says David M. Stalker of Calgene. The group reports its findings in the Oct. 29 Proceedings of the National Academy of Sciences.

 Identification of the genes may enable scientists to genetically alter plants to produce cellulose with more desirable properties. Textile manufacturers have told Calgene, which runs a large cotton-seed business, that "they'd like fibers to be more uniform, stronger, and longer," Stalker says. One day, perhaps, cotton fibers could be made without plants at all, says R. Malcolm Brown Jr. of the University of Texas at Austin, who studies cellulose synthesis in bacteria.

 Brown and his colleagues first isolated cellulose synthase from bacteria in 1989 and a year later identified the gene that encodes it. Even now, scientists do not fully understand the structure and action of the bacterial enzyme.

 To look for matches to parts of the bacterial gene, the Calgene and Hebrew University researchers scanned approximately 400 randomly chosen sequences of DNA from cotton. "We figured that if we screened randomly, we should eventually run across something that looks like synthase," Stalker says. "Some skill was involved and some luck."

 A computer program, usually helpful in finding matches between long stretches of DNA, didn't yield many clues in this case. The plant genes contained two extra DNA regions, which made them dissimilar enough from the bacteria to fool the computer. Instead, the researchers had to just "eyeball" the data, Stalker says. "It was necessary to throw away the computer and let the brain do the work."

 A group at the Australian National University in Canberra has found cellulose-deficient mutants of Arabidopsis thaliana, a simple mustard plant. Stalker expects that these mutant genes will correspond to the genes his group has identified.

 The researchers' immediate plans are to determine whether the genes actually code for cellulose synthase by seeing what they produce when moved into another biological system, such as yeast. Only then might they begin to modify cellulose.