S01 - Session P6 - Changes in the distribution of cell wall hemicelluloses during fruit abscission in olive

Authors: María Carmen Gomez-Jimenez *, Ruben Parra

Although cell-wall modification is believed to underlie the changes in organ abscission, information concerning the changes in cell-wall proteins and hemicellulose polysaccharides is still limited. The aim of this work was to analyze the spationtemporal patterns of the distribution of different extensin proteins and hemicelluloses in the abscission zone (AZ) during natural ripe-fruit abscission in olive ( Olea europaea L.). In this study, we employed immunogold labeling in the ripe-fruit AZ during olive AZ cell separation, using an expanded set of monoclonal antibodies that recognize different types of hemicelluloses (LM11, LM15, and LM21), callose (anti-(1,3)-β-d-glucan) and extensin (JIM19) epitopes, and transmision electron microscopy imaging. Our data demonstrate that AZ cell separation was accompanied by a loss of the JIM19 extensin epitopes and a reduction in the detection of the LM15 xyloglucan epitopes in AZ cell walls, whereas AZ cells were found to be enriched with respect to the xylan and callose levels of the cell wall during olive ripe-fruit abscission. By contrast, AZ cell-wall polysaccharide remodeling did not involve mannans. Moreover, in ripe-fruit AZ, quantitative RT-PCR analysis revealed that OeEXT1 , OeEXT2 , OeXTH9 , and OeXTH13 genes were downregulated during abscission, whereas the expression of OeXTH1 , OeXTH5 , and OeXTH14 g enes increased during abscission. Taken together, the results indicate that AZ cell-wall dynamics during olive ripe-fruit abscission involves extensin protein and hemicellulose modifications, as well as related expressed genes. This is the first study available demonstrating temporal degradation of extensin protein and hemicelluloses in the AZ at the subcellular level. Although cell-wall modification is believed to underlie the changes in organ abscission, information concerning the changes in cell-wall proteins and hemicellulose polysaccharides is still limited. The aim of this work was to analyze the spationtemporal patterns of the distribution of different extensin proteins and hemicelluloses in the abscission zone (AZ) during natural ripe-fruit abscission in olive ( Olea europaea L.). In this study, we employed immunogold labeling in the ripe-fruit AZ during olive AZ cell separation, using an expanded set of monoclonal antibodies that recognize different types of hemicelluloses (LM11, LM15, and LM21), callose (anti-(1,3)-β-d-glucan) and extensin (JIM19) epitopes, and transmision electron microscopy imaging. Our data demonstrate that AZ cell separation was accompanied by a loss of the JIM19 extensin epitopes and a reduction in the detection of the LM15 xyloglucan epitopes in AZ cell walls, whereas AZ cells were found to be enriched with respect to the xylan and callose levels of the cell wall during olive ripe-fruit abscission. By contrast, AZ cell-wall polysaccharide remodeling did not involve mannans. Moreover, in ripe-fruit AZ, quantitative RT-PCR analysis revealed that OeEXT1 , OeEXT2 , OeXTH9 , and OeXTH13 genes were downregulated during abscission, whereas the expression of OeXTH1 , OeXTH5 , and OeXTH14 g enes increased during abscission. Taken together, the results indicate that AZ cell-wall dynamics during olive ripe-fruit abscission involves extensin protein and hemicellulose modifications, as well as related expressed genes. This is the first study available demonstrating temporal degradation of extensin protein and hemicelluloses in the AZ at the subcellular level.