Poster: Root Biology

Abs # 533: A cellulase specific for root cap sloughing in Arabidopsis

Presenter:	del Campillo, Elena , cd84@umail.umd.edu
Authors	del Campillo, Elena  (A)   Ahmed Abd-El-Aziz, Amal  (A)   Crawford, Damian  (A)
Affiliations:	(A): University of Maryland College Park, Dept. Cell Biology and Molecular Genetics

The sloughing of border or root-cap cells from the root tip is important in plant development because it assists the growing root in penetrating the soil. Root cap sloughing is a process of cell-cell separation that entails cell wall breakdown and cellulases are likely to be implicated. Using a promoter-reporter (GUS) construct and RT-PCR analysis, we identified an endo-b-1,4 glucanase (cellulase family 9) of Arabidopsis thaliana that is expressed exclusively in root-cap cells. This cellulase expression begins in the primary root-cap cells when the root reaches around 2 mm in length (24-48 hr post-germination) and continues for at least three weeks. The expression is exclusive to the tips of both primary and secondary roots, and is also detected in cells of the root cap that have been already shed. Seedlings growing under conditions of increased resistance showed an increase in GUS activity in the root tip and a concomitant accumulation in the root-cap cells as they separate from the tip. Expression is inhibited by high concentrations of IAA which cause a deformation and bulging of the root tip and inhibit sloughing of border cells. Similarly, expression is reduced by NPA which induces internal accumulation of IAA. To study the effect of down regulation of this cellulase gene's expression on plant development, we prepared plants harboring antisense and RNAi constructs targeting the 5’UTR and first exon sequence. Overall, these results suggest that this cellulase plays an important role in the sloughing of border cells from the root tip.