Isolation of monoclonal antibodies recognizing xylem cell wall components by using a phage display subtraction method

Monoclonal antibodies (mAbs) recognizing differentiated cell-specific wall components are useful in distinguishing types of cells and dissecting developmental processes. We tried to generate such mAbs using a strategy consisting of (i) isolation of cell walls from synchronously differentiating cells of an in vitro Zinnia culture system, which reflects vascular differentiation in plants (ii) construction of phage display library of recombinant antibody against the cell walls (iii) screening via biopannings with subtractive procedures using non-differentiating cell walls. The advantage of this strategy is that purposive mAbs can be easily screened without purifying antigens of interest. Moreover, this approach can be applied to search for novel subpopulations of cells that are difficult to address by conventional methods because of small subpopulations in heterogeneous mixtures. As a result, we succeeded in isolation of three mAbs, designated CN 8, XD 3, and XD 27. Immunolocalization analyses in Zinnia plants revealed that CN 8 epitope localized in walls of immature tracheary elements (TEs) and xylem parenchyma cells, XD 3 epitope localized in walls of TE precursors and immature fiber cells, and XD 27 epitope localized only in walls of immature TEs. In the Zinnia culture system, these three mAbs distinguished subpopulations of cells in different developmental stages. These results demonstrate that some wall components change dynamically in association with xylem cell differentiation, as cell-surface antigens of animal cells. These mAbs, therefore, are useful as molecular markers to dissect the vascular developmental stage and also as tools to isolate specific xylem cells using a cell sorter.