Evidence that endo-1,4-beta-glucanases act on cellulose in suspension-cultured poplar cells

Suspension-cultured poplar (Populus alba) cells produce two distinct endo-1 ,4-beta-glucanases, one of which is released in the extracellular culture m edium and the other localized in their walls. Two cDNA clones, PopCel1 and PopCel2, isolated from a poplar cDNA library, encode the extracellular and the wall-bound endo-1,4-beta-glucanases, respectively, based upon deduced a mino acid sequences. The products of these two genes contained domains cons erved in endo-1,4-beta-glucanase (family 9) and showed 91.5% amino acid ide ntity. The levels of both PopCel1 and PopCel2 mRNAs increased during the la g phase of growth and decreased rapidly during the linear phase. After the levels had decreased, they were again increased by addition of sucrose to t he culture medium and further enhanced by the addition of 2,4-dichloropheno xyacetic acid (2,4-D) in the presence of sucrose. The accumulation of the m RNAs was correlated with the solubilization of cello-oligosaccharides. Cell o-oligosaccharides and xyloglucan were also solubilized from the wall prepa rations of poplar cells incubated with enzyme preparations from the extrace llular culture medium and walls. An antibody against both PopCel proteins r educed the production of cello-oligosaccharides by the extracellular enzyme by 90% and that by the wall-bound enzyme by 55%, and also prevented xylogl ucan solubilization. The results show that the accumulation of poplar endo- 1,4-beta-glucanases is regulated indirectly by auxin in the presence of suc rose and can act on cellulose in suspension-cultured poplar cells.