Differential expression patterns of two new primary cell wall-related cellulose synthase cDNAs, PtrCesA6 and PtrCesA7 from aspen trees Anita Samuga, Chandrashekhar P. Joshi * Plant Biotechnology Research Center, School of Forest Resources and Environmental Science, Michigan Technological University, 1400, Townsend Drive, Houghton, MI 49931, USA Received 11 November 2003; received in revised form 27 January 2004; accepted 27 February 2004 Available online 5 May 2004 Received by S. Yokoyama Abstract Based on elegant molecular genetic analyses, distinct classes of cellulose synthase (CesA) genes have been associated with either primary or secondary cell wall development in Arabidopsis. Here, we report on cloning of two new CesA cDNAs, PtrCesA6 and PtrCesA7 involved in the primary cell wall development in aspen (Populus tremuloides) trees. Both these distinct cDNAs, isolated from a developing xylem cDNA library, share only 60 –67% identities with each other as well as with five other previously known aspen CesA cDNAs. Interestingly, PtrCESA6 from aspen, a dicot species, shares maximum identity of 81 – 84% with three CESA isoforms from maize and rice, two monocot species. On the other hand, PtrCESA7 shares a maximum identity of 86% with AtCESA2, a primary wall-related CesA member from Arabidopsis, a dicot species. Gene expression analyses by reverse transcriptase-polymerase chain reactions (RT-PCRs) suggested that both these genes are expressed at a low level in all aspen tissues examined but PtrCesA7 is expressed at a higher level than PtrCesA6. While corroborating these results, in situ mRNA hybridization studies using three different aspen organs also suggested that PtrCesA6 and PtrCesA7 genes are expressed in all expanding cells depositing primary cell wall but PtrCesA7 is expressed at a higher level than PtrCesA6. These differential gene expression profiles suggest that each of these CesAs may be playing a specific role during primary cell wall development in aspen trees. Isolation of two primary wall related CesA genes from xylem tissues also suggest their importance during xylem development, which is traditionally considered to be enriched in secondary cell wall forming cells of economical significance. D 2004 Elsevier B.V. All rights reserved. Keywords: Aspen; Cellulose biosynthesis; CesA; In situ hybridization; Wood 1. Introduction Cellulose is an integral component of plant cell walls. It is also of great economic value due to its abundance and structural characteristics. In primary cell walls of trees, cellulose contributes to about 20–30% in dry weight, whereas secondary cell walls contain f 40 – 50% cellulose (Mellerowicz et al., 2001). Cellulose microfibrils of prima- ry walls also control the size and shape of plant cells. Cellulose microfibril orientation in meristematic tissues affects organ initiation thus influencing the architecture of the whole plant (Green, 1994). As compared to primary cell walls, secondary cell walls with greater cellulose crystal- linity, higher degree of polymerization and better organized cellulose microfibrils provide mechanical strength and rigidity to entire plant. Secondary cell walls of trees or wood in particular offer major resource of raw materials to paper and wood-based forest product industries. Paradoxically, in contrast to cellulose abundance and its plethora of uses, we know little about the molecular processes involved in cellulose biosynthesis in plants. Characterization of cotton cellulose synthase ( CesA) cDNAs provided the first glimpse of plant CESA protein structure (Pear et al., 1996). Molecular approaches coupled with availability of genome sequence information eventu- ally identified a large family of at least 10 CesA genes in 0378-1119/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.gene.2004.02.057 Abbreviations: CesA, cellulose synthase gene/cDNA; CESA, cellulose synthase protein; HVR, hypervariable region; RT-PCR, reverse transcrip- tase-polymerase chain reaction. * Corresponding author. Tel.: +1-906-487-3480; fax: +1-906-487- 2915. E-mail address: cpjoshi@mtu.edu (C.P. Joshi). www.elsevier.com/locate/gene Gene 334 (2004) 73 – 82