Planta (2006) 224: 828–837 DOI 10.1007/s00425-006-0269-1 ORIGINAL ARTICLE Suchita Bhandari · Takeshi Fujino Shiv Thammanagowda · Dongyan Zhang · Fuyu Xu Chandrashekhar P. Joshi Xylem-specific and tension stress-responsive coexpression of KORRIGAN endoglucanase and three secondary wall-associated cellulose synthase genes in aspen trees Received: 14 January 2006 / Accepted: 10 March 2006 / Published online: 31 March 2006  Springer-Verlag 2006 Abstract In nature, angiosperm trees develop tension wood on the upper side of their leaning trunks and drooping branches. Development of tension wood is one of the straightening mechanisms by which trees counter- act leaning or bending of stem and resume upward growth. Tension wood is characterized by the develop- ment of a highly crystalline cellulose-enriched gelatinous layer next to the lumen of the tension wood Wbers. Thus experimental induction of tension wood provides a sys- tem to understand the process of cellulose biosynthesis in trees. Since KORRIGAN endoglucanases (KOR) appear to play an important role in cellulose biosynthesis in Arabidopsis, we cloned PtrKOR, a full-length KOR cDNA from aspen xylem. Using RT-PCR, in situ hybrid- ization, and tissue-print assays, we show that PtrKOR gene expression is signiWcantly elevated on the upper side of the bent aspen stem in response to tension stress while KOR expression is signiWcantly suppressed on the oppo- site side experiencing compression stress. Moreover, three previously reported aspen cellulose synthase genes, namely, PtrCesA1, PtrCesA2, and PtrCesA3 that are closely associated with secondary cell wall development in the xylem cells exhibited similar tension stress-respon- sive behavior. Our results suggest that coexpression of these four proteins is important for the biosynthesis of highly crystalline cellulose typically present in tension wood Wbers. Their simultaneous genetic manipulation may lead to industrially relevant improvement of cellu- lose in transgenic crops and trees. Keywords Aspen · Cellulose · Cellulose synthase · KORRIGAN endoglucanase · Tension wood · Trees Abbreviations CesA: Cellulose synthase · KOR: Korrigan endoglucanase · DP: Degree of polymerization · EGase: Endoglucanase Introduction Since cellulose is an important component of plant cell walls, genetic modulation of cellulose synthesis can have a direct impact on several aspects of plant growth and development (Somerville et al. 2004) including, but not limited to, cell division and expansion, plant morphogen- esis, and plant responses to the environment. Therefore, a thorough understanding of the intricacies of the cellu- lose biosynthetic processes is pivotal for future experi- ments targeting genetic improvement of cellulose production in economically important plants (Delmer 1999; Doblin et al. 2002; Williamson et al. 2002; Joshi et al. 2004). However, this Weld has recently witnessed many interesting yet contrasting situations. Although cellulose is the most abundant biopolymer on earth, the Wrst plant cellulose synthase (CesA) gene was reported only recently (Pear et al. 1996). Chemically, cellulose is a polymer of -1,4–linked glucose and this simple structure is conserved among all plants; yet at least two diVerent groups of CesA proteins are involved in cellulose deposi- tion during primary and secondary wall formation (Doblin et al. 2002). These two types of cell walls also greatly diVer in the quantity and quality of cellulose they possess in terms of degree of polymerization (DP), crys- tallinity, and microWbril orientation (Joshi et al. 2004). Therefore, it is possible that CesA proteins play a major Suchita Bhandari and Takeshi Fujino contributed equally to this research. S. Bhandari · T. Fujino · S. Thammanagowda · D. Zhang F. Xu · C. P. Joshi (&) Biotechnology Research Center, School of Forest Resources and Environmental Sciences, Michigan Technological University, Houghton, MI 49931, USA E-mail: cpjoshi@mtu.edu Tel.: +1-906-4873480 Fax: +1-906-4872915 Present address: S. Bhandari BILT, First India Place, Tower C, Mehrauli-Gurgaon Road, Gurgaon, Haryana 122002, India