Minisymposium 5: Cell Walls

Abs # 15004: Coordinate expression of three cellulose synthase genes may orchestrate cellulose biosynthesis during the wood formation in aspen trees

Presenter:	Joshi, Chandrashekhar P., cpjoshi@mtu.edu
Authors	Joshi, Chandrashekhar P. (A)   Liang, Xiaoe  (A)   Samuga, Anita  (A)   Kalluri, Udaya  (A)
Affiliations:	(A): School of Forest Resources and Environmental Science, Michigan Technological University
Web Site:	http://forest.mtu.edu/faculty/joshi/

Secondary cell walls of woody trees provide valuable resources for a variety of forest products. Biotechnological improvement of cell wall components of trees, therefore, holds an enormous promise for forest product industries. Our long-term goal is to decipher the biosynthetic mechanisms of major cell wall polymers in trees in order to genetically improve them for better wood utilization. Cellulose biosynthesis is one of the most economically important but least understood biological processes that plants have been performing for over billion years. But the first cellulose synthase (CesA) gene from plants was cloned and characterized only in 1996. Recent molecular genetic evidence strongly suggests that plant genomes host a rather large family of CesA genes and multiple but distinct CesA proteins are involved in primary and secondary cell wall formation in Arabidopsis. In order to evaluate whether the mechanism of cellulose biosynthesis is conserved between Arabidopsis and trees, we isolated three distinct secondary wall-related CesA genes from aspen trees namely, PtrCesA1, PtrCesA2 and PtrCesA3 where encoded proteins shared a high degree of similarity (>85%) with Arabidopsis AtCesA8, AtCesA7 and AtCesA4 gene products implicated in secondary cell wall formation. In situ mRNA hybridization experiments exclusively localized PtrCesA1, PtrCesA2 and PtrCesA3 transcripts in the same developing xylem and phloem fiber cells of aspen stems suggesting that their coordinate expression might be germane for proper cellulose deposition during wood formation. Moreover, the same three genes are simultaneously upregulated in tension stress-responsive manner on the upper side of bent stem and coordinately downregulated on the lower side of bent stem mimicking the tension wood formation in angiosperm trees during which large quantities of highly crystalline cellulose are produced in tension wood fibers. Most interestingly, the three other aspen CesA genes, PtrCesA4, PtrCesA5 and PtrCesA6 sharing a high degree of similarity with Arabidopsis CesA genes involved in primary cell wall formation do not show such xylem-specific and tension stress-responsive behavior. These results strongly suggest that simultaneous upregulation of the three types of secondary cell wall-related CesAs may be required to obtain a desired outcome of increased production of better quality cellulose in woody trees that will have a tremendous impact on global forest product industries.