Functional Analysis of the Arlequin Mutant Corroborates the Essential Role of the ARLEQUIN/TAGL1 Gene during Reproductive Development of Tomato

Abstract

Reproductive development of higher plants comprises successive events of organ differentiation and growth which finally lead to the formation of a mature fruit. However, most of the genetic and molecular mechanisms which coordinate such developmental events are yet to be identified and characterized. Arlequin (Alq), a semi-dominant T-DNA tomato mutant showed developmental changes affecting flower and fruit ripening. Sepals were converted into fleshy organs which ripened as normal fruit organs and fruits displayed altered ripening features. Molecular characterization of the tagged gene demonstrated that it corresponded to the previously reported TOMATO AGAMOUS-LIKE 1 (TAGL1) gene, the tomato ortholog of SHATTERPROOF MADS-box genes of Arabidopsis thaliana, and that the Alq mutation promoted a gain-of-function phenotype caused by the ectopic expression of TAGL1. Ectopic overexpression of TAGL1 resulted in homeotic alterations affecting floral organ identity that were similar to but stronger than those observed in Alq mutant plants. Interestingly, TAGL1 RNAi plants yielded tomato fruits which were unable to ripen. They displayed a yellow-orange color and stiffness appearance which are in accordance with reduced lycopene and ethylene levels, respectively. Moreover, pericarp cells of TAGL1 RNAi fruits showed altered cellular and structural properties which correlated to both decreased expression of genes regulating cell division and lignin biosynthesis. Over-expression of TAGL1 is able to rescue the non-ripening phenotype of rin and nor mutants, which is mediated by the transcriptional activation of several ripening genes. Our results demonstrated that TAGL1 participates in the genetic control of flower and fruit development of tomato plants. Furthermore, gene silencing and over-expression experiments demonstrated that the fruit ripening process requires the regulatory activity of TAGL1. Therefore, TAGL1 could act as a linking factor connecting successive stages of reproductive development, from flower development to fruit maturation, allowing this complex process to be carried out successfully.

TomatoFRUITFULLhomologs regulate fruit ripening via ethylene biosynthesis

“…A similar phenotype was found in TAGL1 silenced tomatoes, which also showed reduced firmness although ethylene production and lycopene accumulation were defective, and reduced pericarp thickness and the thinner cuticle layer were postulated as a possible explanation of the softening. 16,18) We observed lower expression of the genes involved in cuticle biosynthesis in the pre-ripening stage fruit of the suppressed line. FUL2 is expressed strongly at the pre-ripening stage, but FUL1 is not, 20) suggesting that FUL2 is responsible for cuticle biosynthesis before ripening.…”

“…These phenotypes in the FUL1/FUL2 suppressed fruits, a failure of ripening but reduced firmness, were similar to TAGL1 suppressed lines. [16][17][18] Because TAGL1 suppression reduced the accumulation of cuticle on the peel, 16,18) we analyzed cuticle accumulation in the FUL1/FUL2 suppressed fruits. We found that the FUL1/FUL2 suppressed fruits had a thinner layer of cuticle than the rin mutant fruits (Fig.…”

“…These efforts identified TAGL1, a MADSbox gene encoding a SHATTERPROOF (SHP) homolog, as a regulator of fruit ripening through ethylene production. [16][17][18] Additionally, Bemer et al 19) reported that two MADS-box genes encoding FRUITFULL homologs (FUL1 and FUL2, previously called TDR4 and SlMBP7, respectively) redundantly regulate fruit ripening. They reported that, unlike ripening regulation by RIN and TAGL1, the FUL homologs regulate only ethylene-independent ripening, because their transgenic lines, containing an RNAi construct designed to suppress FUL1 and FUL2, produced ethylene at levels equal to the wild type.…”

Variations on a theme in fruit development: the PLE lineage of MADS-box genes in tomato (TAGL1) and other species

“…Using RNA interference (RNAi), transgenic plants with reduced TAGL1 expression produced fruit that showed varying degrees of defects in ripening (Vrebalov et al 2009;Pan et al 2010;Gimenez et al 2010). Similar ripening phenotypes were observed in a study utilizing virus-induced gene silencing and an ERF-associated amphiphilic repression motif to overexpress TAGL1 as a dominant repressor (Itkin et al 2009).…”

“…Several studies over the past few years have examined the role of the TAGL1 gene in controlling many aspects of tomato fruit ripening (Itkin et al 2009;Vrebalov et al 2009;Pan et al 2010;Pineda et al 2010;Gimenez et al 2010Gimenez et al , 2015Gimenez et al , 2016. Using RNA interference (RNAi), transgenic plants with reduced TAGL1 expression produced fruit that showed varying degrees of defects in ripening (Vrebalov et al 2009;Pan et al 2010;Gimenez et al 2010).…”