Suppression of a Prolyl 4 Hydroxylase Results in Delayed Abscission of Overripe Tomato Fruits

Abstract

The tomato pedicel abscission zone (AZ) is considered a model system for flower and fruit abscission development, activation, and progression. O-glycosylated proteins such as the Arabidopsis IDA (INFLORESCENCE DEFICIENT IN ABSCISSION) peptide and Arabinogalactan proteins (AGPs) which undergo proline hydroxylation were demonstrated to participate in abscission regulation. Considering that the frequency of occurrence of proline hydroxylation might determine the structure as well the function of such proteins, the expression of a tomato prolyl 4 hydroxylase, SlP4H3 ( Solanum lycopersicum Prolyl 4 Hydroxylase 3) was suppressed in order to investigate the physiological significance of this post-translational modification in tomato abscission. Silencing of SlP4H3 resulted in the delay of abscission progression in overripe tomato fruits 90 days after the breaker stage. The cause of this delay was attributed to the downregulation of the expression of cell wall hydrolases such as SlTAPGs (tomato abscission polygalacturonases) and cellulases as well as expansins. In addition, minor changes were observed in the mRNA levels of two SlAGPs and one extensin. Moreover, structural changes were observed in the silenced SlP4H3AZs. The fracture plane of the AZ was curved and not along a line as in wild type and there was a lack of lignin deposition in the AZs of overripe fruits 30 days after breaker. These results suggest that proline hydroxylation might play a role in the regulation of tomato pedicel abscission.

High-Throughput Genotyping of Resilient Tomato Landraces to Detect Candidate Genes Involved in the Response to High Temperatures

“…The first gene, Solyc01g017220, coding for an ATP synthase epsilon chain, is reported to be involved in drought stress responses [ 47 ]. The genes Solyc02g070280 , which codes for a protein involved in the transport of amino acids during the pedicel abscission [ 48 ], and Solyc07g053640 , which codes for an arabinogalactan-protein that could be involved in abscission events [ 49 ], might impact on FS. This is a yield-related trait highly affected by high temperatures.…”

The role of arabinogalactan proteins (AGPs) in fruit ripening—a review

“…The pleiotropic character of P4Hs mutations reveals also the functional importance of AGPs with respect to growth and development. Genetic mutant analysis of tomato P4Hs transgenic lines indicates the importance of the Agp’s content and possibly their glycan chains for the differentiation and development of fruit abscission fracture plane as well as the progression of the natural abscission process 18 . For the first time in tomato, alterations in the function of post-translational modification such as proline hydroxylation revealed the significance of AGPs glycosylation in the differentiation of fruit abscission zone 18 .…”

“…Microscopic studies of abscission zones showed anatomical alterations in mutant fruit, i.e. variations in the numbers of parenchymal layers indicating cells detained in an undifferentiated stage as well as disruption in lignin deposition 18 .…”

“…Moreover, in the stable independent transgenic lines with suppressed expression of Solanum lycopersicum Prolyl 4 Hydroxylase 3 - SlP4H3, abscission specific cell wall hydrolases, i.e., polygalacturonase and cellulases were downregulated leading to the prolongation of overripe fruit abscission 18 . These data imply that the manipulation of post-translational alterations might induce changes in the transcriptional activation of a significant number of genes indicating putative regulation of transcription factors and/or involvement of regulatory AGPs.…”

“…Glycosylation of AGPs constitutes the basis of their essential function and while the molecular mechanisms underlying the function and metabolism of cell wall polysaccharides are well known, the role of AGPs as structural-functional proteoglycans in fruit ripening is described only in several experimental data. The involvement of AGPs in abscission zone differentiation and organ detachment progression is currently under investigation indicating that AGPs might play a regulatory role 18 . Considering that cell wall dissolution is necessary for both fruit softening and abscission zone cell separation to occur it is possible that AGPs might also play a regulatory role in fruit ripening progression.…”