Abstract
Plant cellulose synthases (CesAs) are the key enzymes necessary for cellulose biosynthesis. In Arabidopsis, two distinct groups of three CesAs each are necessary for cellulose synthesis during primary and secondary cell wall formation. It has also been suggested that such three CesAs interact with each other to form plasma-membrane bound rosette complexes that are functional during cellulose production. However, in vivo demonstration of such assemblies of three CesAs into rosettes has not been possible. We used yeast two-hybrid assays to demonstrate the possible interactions among several CesAs from Arabidopsis and aspen via their N-terminal zinc-binding domains (ZnBDs). While strong positive interactions were detected among ZnBDs from secondary wall associated CesAs of both Arabidopsis and aspen, the intergeneric interactions between Arabidopsis and aspen CesAs were weak. Moreover, in aspen, three primary wall associated CesA ZnBDs positively interacted with each other as well as with secondary CesAs. These results suggest that ZnBDs from either primary or secondary CesAs, and even from different plant species could interact but are perhaps insufficient for specificities of such interactions among CesAs. These observations suggest that some other more specific interacting regions might exist within CesAs. It is also possible that some hitherto unknown mechanism exists in plants for assembling the rosette complexes with different compositions of CesAs. Understanding how cellulose is synthesized will have a direct impact on utilization of lignocellulosic biomass for bioenergy production.
Highlights
Cellulose, the most abundant renewable biopolymer on earth, has a great potential to be used as a major raw material for bioenergy production
Previous genetic experiments with three cellulose synthesis-defective mutants from Arabidopsis, namely, irx1, irx3, and irx5 exhibiting irregular xylem phenotypes have suggested that the presence of at least three secondary cellulose synthases (CesAs) is essential for cellulose biosynthesis in secondary cell wall forming cells [9,10,11]
We first set out to determine whether zinc-binding domains (ZnBDs) from AtCesA4, 7 and 8 can physically interact with each other and whether they are capable of forming homo- as well as heterodimers in the Y2H system
Summary
The most abundant renewable biopolymer on earth, has a great potential to be used as a major raw material for bioenergy production. A better understanding of the process of cellulose biosynthesis will, have a far-reaching impact on agricultural and forest product industries that utilize cellulose as a main raw material. The precise molecular mechanism of cellulose biosynthesis has so far eluded scientists for a long time [3], and it is still unclear how plasma membrane bound CesA complexes regulate economically important characteristics of cellulose such as degree of polymerization, microfibril angle and crystallinity. It has been suggested that large enzyme complexes (> 500 kDa) consisting of 36 CesA subunits, arranged in the form of rosettes, synthesize about 36 glucan fibers-thick cellulose microfibrils at the plasma membrane [4]. Based on immunogold labeling experiments, CesAs appear to be a component of rosette complexes [5] actual visualization of the 36 CesAs present in the rosettes has never been possible due to substantial technical limitations [6]
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