The Auxin Sl-IAA17 Transcriptional Repressor Controls Fruit Size Via the Regulation of Endoreduplication-Related Cell Expansion

Abstract

Auxin is known to regulate cell division and cell elongation, thus controlling plant growth and development. Part of the auxin signaling pathway depends on the fine-tuned degradation of the auxin/indole acetic acid (Aux/IAA) transcriptional repressors. Recent evidence indicates that Aux/IAA proteins play a role in fruit development in tomato (Solanum lycopersicum Mill.), a model species for fleshy fruit development. We report here on the functional characterization of Sl-IAA17 during tomato fruit development. Silencing of Sl-IAA17 by an RNA interference (RNAi) strategy resulted in the production of larger fruit than the wild type. Histological analyses of the fruit organ and tissues demonstrated that this phenotype was associated with a thicker pericarp, rather than larger locules and/or a larger number of seeds. Microscopic analysis demonstrated that the higher pericarp thickness in Sl-IAA17 RNAi fruits was not due to a larger number of cells, but to the increase in cell size. Finally, we observed that the cell expansion in the transgenic fruits is tightly coupled with higher ploidy levels than in the wild type, suggesting a stimulation of the endoreduplication process. In conclusion, this work provides new insights into the function of the Aux/IAA pathway in fleshy fruit development, especially fruit size and cell size determination in tomato.

SCFTIR1/AFB-Based Auxin Perception: Mechanism and Role in Plant Growth and Development

“…On the other hand, the analysis of loss-of-function mutants has so far failed to reveal robust mutant phenotypes in Arabidopsis, suggesting extensive genetic redundancy among members of the family (Remington et al, 2004;Overvoorde et al, 2005;reviewed in Reed, 2001). This is in contrast to the situation in tomato (Solanum lycopersicum) where several loss-of-function alleles or antisense constructs produce a robust phenotype suggesting that there is less redundancy in this species (Wang et al, 2005;Chaabouni et al, 2009;Bassa et al, 2012;Deng et al, 2012;Su et al, 2014).…”

The Aux/IAA, Sl-IAA17 regulates quality parameters over tomato fruit development

“…1,2 Unlike the situation in the model plant Arabidopsis where the functional significance of Aux/ IAAs was mainly gained by the analysis of gain-of-function mutants, uncovering the function in planta of tomato Aux/IAAs was mainly achieved through the characterization of downregulated lines. 3 and refs herein; [4][5][6][7] In particular, we have recently shown that down-regulation of Sl-IAA17 gene in tomato results in fruits with higher weight and thicker pericarp, probably as a result of enhanced cell expansion linked to an increased endoreduplication rate. 7 We report here on additional phenotypes related to fruit ripening traits uncovered in these Sl-IAA17 downregulated lines.…”

“…3 and refs herein; [4][5][6][7] In particular, we have recently shown that down-regulation of Sl-IAA17 gene in tomato results in fruits with higher weight and thicker pericarp, probably as a result of enhanced cell expansion linked to an increased endoreduplication rate. 7 We report here on additional phenotypes related to fruit ripening traits uncovered in these Sl-IAA17 downregulated lines.…”

“…Figure 1A shows that the soluble solid content (SSC) was higher in downregulated lines than in WT at the red stage (7 d after breaker), this difference being significant in the 2 lines displaying the strongest downregulation of Sl-IAA17. 7 Recently, it has been observed that Sl-ARF4 under-expressing lines displaye higher soluble solids content at the ripening stages 8 along with more starch accumulation and higher expression at the transcript level of the AGPase known to regulate the early step of starch synthesis. 9 Interestingly, it has been observed that Sl-IAA17 protein is able to interact with several ARF proteins among which Sl-ARF4, Sl-ARF5, Sl-ARF6, Sl-ARF7 and Sl-ARF8.…”

“…This morphology parameter describes the angle of the fruit tip. The larger distal angle in Sl-IAA17 down-regulated lines may be connected to the larger fruit size of the RNAi lines, 7 which look like well inflated balloons with a very round shape. This morphological trait could also be linked to the acceleration of the flower cap abscission (unpublished results).…”