Type III Glycine Rich Proteins Promote Early callogenesis in Crocus sativus L.

Endogenously expressed Glycine Rich Proteins (GRPs) play a pivotal role in plant cell development and differentiation. In this study, we investigated the effect of exogenously supplemented GRPs on Crocus sativus L. cultures.  We are first to report the effect of exogenously supplemented GRPs on callus induction. Explants grown in GRP supplemented media showed callus induction much earlier than those grown without GRP supplementation. To the contrary, sub-cultured callus or single cell suspension culture were not affected by GRP supplementation. Immunofluorescence experiments showed a possible cell wall-GRP interaction with highest interaction in corm tissue compared to either callus or suspension cells. To evaluate the specificity of the GRP-cell wall interaction, matrix binding assay was set up. GRPs showed little or no binding affinity with either total protein extract or cell wall proteins specifically. However, GRPs showed a high binding affinity with pectin fractions of cell wall purified from Crocus corms or synthetic pectin. Our finding suggests that the exogenously supplemented GRPs bind with cell wall matrix of the corm possibly through a protein-polysaccharide interaction that might be responsible for inducing an early-stage callogenesis.