Alq mutation increases fruit set rate and allows the maintenance of fruit yield under moderate saline conditions

New Advances in the Study of Regulation of Tomato Flowering-Related Genes Using Biotechnological Approaches

The tomato is a convenient object for studying reproductive processes, which has become a classic. Such complex processes as flowering and fruit setting require an understanding of the fundamental principles of molecular interaction, the structures of genes and proteins, the construction of signaling pathways for transcription regulation, including the synchronous actions of cis-regulatory elements (promoter and enhancer), trans-regulatory elements (transcription factors and regulatory RNAs), and transposable elements and epigenetic regulators (DNA methylation and acetylation, chromatin structure). Here, we discuss the current state of research on tomatoes (2017-2023) devoted to studying the function of genes that regulate flowering and signal regulation systems using genome-editing technologies, RNA interference gene silencing, and gene overexpression, including heterologous expression. Although the central candidate genes for these regulatory components have been identified, a complete picture of their relationship has yet to be formed. Therefore, this review summarizes the latest achievements related to studying the processes of flowering and fruit set. This work attempts to display the gene interaction scheme to better understand the events under consideration.

Hormonal interactions underlying parthenocarpic fruit formation in horticultural crops

In some horticultural crops, such as Cucurbitaceae, Solanaceae, and Rosaceae species, fruit set and development can occur without the fertilization of ovules, a process known as parthenocarpy. Parthenocarpy is an important agricultural trait that can not only mitigate fruit yield losses caused by environmental stresses but can also induce the development of seedless fruit, which is a desirable trait for consumers. In the present review, the induction of parthenocarpic fruit by the application of hormones such as auxins (2,4 dichlorophenoxyacetic acid; naphthaleneacetic acid), cytokinins (forchlorfenuron; 6-benzylaminopurine), gibberellic acids, and brassinosteroids is first presented. Then, the molecular mechanisms of parthenocarpic fruit formation, mainly related to plant hormones, are presented. Auxins, gibberellic acids, and cytokinins are categorized as primary players in initiating fruit set. Other hormones, such as ethylene, brassinosteroids, and melatonin, also participate in parthenocarpic fruit formation. Additionally, synergistic and antagonistic crosstalk between these hormones is crucial for deciding the fate of fruit set. Finally, we highlight knowledge gaps and suggest future directions of research on parthenocarpic fruit formation in horticultural crops.

The interplay between ABA/ethylene and NAC TFs in tomato fruit ripening: a review

This review contains functional roles of NAC transcription factors in the transcriptional regulation of ripening in tomato fruit, describes the interplay between ABA/ethylene and NAC TFs in tomato fruit ripening. Fruit ripening is regulated by a complex network of transcription factors (TFs) and genetic regulators in response to endogenous hormones and external signals. Studying the regulation of fruit ripening has important significance for controlling fruit quality, enhancing nutritional value, improving storage conditions and extending shelf-life. Plant-specific NAC (named after no apical meristem (NAM), Arabidopsis transcription activator factor 1/2 (ATAF1/2) and Cup-shaped cotyledon (CUC2)) TFs play essential roles in plant development, ripening and stress responses. In this review, we summarize the recent progress on the regulation of NAC TFs in fruit ripening, discuss the interactions between NAC and other factors in controlling fruit development and ripening, and emphasize how NAC TFs are involved in tomato fruit ripening through the ethylene and abscisic acid (ABA) pathways. The signaling network regulating ripening is complex, and both hormones and individual TFs can affect the status or activity of other network participants, which can alter the overall ripening network regulation, including response signals and fruit ripening. Our review helps in the systematic understanding of the regulation of NAC TFs involved in fruit ripening and provides a basis for the development or establishment of complex ripening regulatory network models.

SlTPL1 Silencing Induces Facultative Parthenocarpy in Tomato

Facultative parthenocarpy is of great practical value. However, the molecular mechanism underlying facultative parthenocarpy remains elusive. Transcriptional co-repressors (TPL) act as a central regulatory hub controlling all nine phytohormone pathways. Previously, we proved that SlTPLs participate in the auxin signaling pathway by interacting with auxin/indole acetic acid (Aux/IAAs) in tomato; however, their function in fruit development has not been studied. In addition to their high expression levels during flower development, the interaction between SlTPL1 and SlIAA9 stimulated the investigation of its functional significance via RNA interference (RNAi) technology, whereby the translation of a protein is prevented by selective degradation of its encoded mRNA. Down-regulation of SlTPL1 resulted in facultative parthenocarpy. Plants of SlTPL1-RNAi transgenic lines produced similar fruits which did not show any pleiotropic effects under normal conditions. However, they produced seedless fruits upon emasculation and under heat stress conditions. Furthermore, SlTPL1-RNAi flower buds contained higher levels of cytokinins and lower levels of abscisic acid. To reveal how SlTPL1 regulates facultative parthenocarpy, RNA-seq was performed to identify genes regulated by SlTPL1 in ovaries before and after fruit set. The results showed that down-regulation of SlTPL1 resulted in reduced expression levels of cytokinin metabolism-related genes, and all transcription factors such as MYB, CDF, and ERFs. Conversely, down-regulation of SlTPL1 induced the expression of genes related to cell wall and cytoskeleton organization. These data provide novel insights into the molecular mechanism of facultative tomato parthenocarpy and identify SlTPL1 as a key factor regulating these processes.

How Hormones and MADS-Box Transcription Factors Are Involved in Controlling Fruit Set and Parthenocarpy in Tomato

Fruit set is the earliest phase of fruit growth and represents the onset of ovary growth after successful fertilization. In parthenocarpy, fruit formation is less affected by environmental factors because it occurs in the absence of pollination and fertilization, making parthenocarpy a highly desired agronomic trait. Elucidating the genetic program controlling parthenocarpy, and more generally fruit set, may have important implications in agriculture, considering the need for crops to be adaptable to climate changes. Several phytohormones play an important role in the transition from flower to fruit. Further complexity emerges from functional analysis of floral homeotic genes. Some homeotic MADS-box genes are implicated in fruit growth and development, displaying an expression pattern commonly observed for ovary growth repressors. Here, we provide an overview of recent discoveries on the molecular regulatory gene network underlying fruit set in tomato, the model organism for fleshy fruit development due to the many genetic and genomic resources available. We describe how the genetic modification of components of this network can cause parthenocarpy, discussing the contribution of hormonal signals and MADS-box transcription factors.

GREEN STRIPE, encoding methylated TOMATO AGAMOUS-LIKE 1, regulates chloroplast development and Chl synthesis in fruit

Fruit development involves chloroplast development, carotenoid accumulation and fruit coloration. Although genetic regulation of fruit development has been extensively investigated, epigenetic regulation of fruit coloration remains largely unexplored. Here, we report a naturally occurring epigenetic regulation of TAGL1, and its impact on chloroplast development and fruit coloration. We used a genome-wide association study in combination with map-based cloning to identify the GREEN STRIPE (GS) locus, a methylated isoform of TAGL1 regulating diversified chloroplast development and carotenoid accumulation. Nonuniform pigmentation of fruit produced by GS was highly associated with methylation of the TAGL1 promoter, which is linked to a SNP at SL2.50ch07_63842838. High degrees of methylation of the TAGL1 promoter downregulated its expression, leading to green stripes. By contrast, low degrees of methylation led to light green stripes in gs. RNA-seq and ChIP collectively showed that the expression of genes involved with Chl synthesis and chloroplast development were significantly upregulated in green stripes relative to light green stripes. Quantitative PCR and dual luciferase assay confirmed that TAGL1 downregulates expression of SlMPEC, SlPsbQ, and SlCAB, and upregulates expression of PSY1 - genes which are associated with chloroplast development and carotenoid accumulation. Altogether, our findings regarding the GS locus demonstrate that naturally occurring methylation of TAGL1 has diverse effects on plastid development in fruit.