Antibodies against a Gossypium hirsutum recombinant cellulose synthase (Ces A) specifically label cellulose synthase in Micrasterias denticulata

Abstract

Using immunocytochemistry combined with light and electron microscopy, antibodies against cotton (Gossypium hirsutum) Ces A3 were used to identify and localize Ces A proteins in Micrasterias denticulata. Silver-enhanced, immuno-gold labeling of Ces A was localized on the plasma membrane with light and immuno-electron microscopy. Immuno-gold labeling of $\beta$-1,4-glucan synthase always was observed in contact with the tips of negatively stained cellulose microfibrils. Although the $\beta$-1,4-glucan synthesizing system in the cell wall of Micrasterias denticulata has been investigated by several methods in the past few decades, these results provide the first significant evidence that the hexagonal arrays of ‘rosettes’ observed in the freeze-etch replica techniques within the plasma membrane of Micrasterias denticulata are $\beta$-1, 4-glucan synthases. In addition, the antibodies to cotton Ces A3 show no reactivity with $\beta$-1,4-glucan synthases from Boergesenia forbesii (a Siphonocladaceaen alga with linear terminal complexes=TCs). These results suggest that the specific morphology of TCs (e.g., rosette or linear arrangement) is closely related to the cellulose synthase antibody binding sites (catalytic domains). These data are consistent with a recent phylogenic analysis which shows that Mesotaenium caldariorum possesses Ces A-type genes that are closely related to Ces A’s in vascular plants. This report suggests a significant divergence between the cellulose synthase catalytic subunits of the Chlorophyta (linear TCs) and the Streptophyta (rosette TCs).