Down-regulation of an auxin response factor in the tomato alters pericap tissue architecture and cell wall polysaccharide.
Lahayt M., Guillon F., Bouchet B., Devaux M.F., Frasse P., Bouzayen M.
5th International Postharvest Symposium . Volume of Abstract . Verona, Italy 6-11 June 2004. page 4
2004
บทคัดย่อ
Down-regulation of an auxin response factor in the tomato alters pericap tissue architecture and cell wall polysaccharide.
The understanding of fruit texture elaboration markedly benefit from studies of transgenic plants affected in the expression of enzymes and proteins responsible for cell wall(CW) polymers remodelling during ripening.The latter event is mainly orchestrated by hormones such as ethylene through the intervention of transcription factors.In tomato, down regulation of an auxin response factor (DR12) regulated by ethylene resulted in a pleiotropic phenotype including enhanced fruit firmness and blotchy ripening (Jone et al. 2002, Plant J. 32: 603-613).To uncover the molecular basis of this enhanced firmness, biochemical and structural characterizations of the pericarp CW polysaccharides from DR12 MG and RR transgenic fruits were carried out and compared to WT fruit.Acetyl-esterification (DA) of polysaccharides was higher in DR12 fruit compared to WT at both ripening stages.Methyl esterification (DM) of pectins in DR12 was slightly higher for the MG and lower for the RR stages.CW polysaccharide composition showed a decrease in pectin DM and galactan in RR DR12 and WT fruits.An increased water and oxalate extraction of pectins was observed for RR DR12 and WT fruits.However, endopolygalacturonase degradation and competitive ELISA assays of the water and oxalate pectins differed between WT and DR12.Quantitative microscopic analysis showed that on an area basis, 9% of the DR12 outer cortical region corresponded to cells of Æ < 50 mm compared to 7% in WT.Immuno-cytochemical analyses using monoclonal antibodies against different pectic epitops supported the physico-chemical data.Thus, DR12 down-regulation does not impair pectin de-assembly during ripening but seems to affect cell division, pectin methyl esterification and polysaccharide acetyl esterification.Whether the latter correspond to hemicelluloses is still to be elucidated.The increased firmness of the RR mutant fruit appears to involve increased pectic CW interactions and peculiar tissue architectrue.