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Summary: The plant hormone ethylene plays a critical role in fruit defense against Botrytis cinerea attack, but the underlying mechanisms remain poorly understood. Here, we showed that ethylene response factor SlERF.C1 acts as a key regulator to trigger the ethylene‐mediated defense against B. cinerea in tomato fruits without compromising ripening.Knockout of SlERF.C1 increased fruit susceptibility to B. cinerea with no effect on ripening process, while overexpression enhanced resistance. RNA‐Seq, transactivation assays, EMSA and ChIP‐qPCR results indicated that SlERF.C1 activated the transcription of PR genes by binding to their promoters.Moreover, SlERF.C1 interacted with the mitogen‐activated protein kinase SlMPK8 which allowed SlMPK8 to phosphorylate SlERF.C1 at the Ser174 residue and increases its transcriptional activity. Knocking out of SlMPK8 increased fruit susceptibility to B. cinerea, whereas overexpression enhanced resistance without affecting ripening. Furthermore, genetic crosses between SlMPK8‐KO and SlERF.C1‐OE lines reduced the resistance to B. cinerea attack in SlERF.C1‐OE fruits. In addition, B. cinerea infection induced ethylene production which in turn triggered SlMPK8 transcription and enhanced the phosphorylation of SlERF.C1.Overall, our findings reveal the regulatory mechanism of the 'Ethylene‐MPK8‐ERF.C1‐PR' module in resistance against B. cinerea and provide new insight into the manipulation of gray mold disease in fruits. [ABSTRACT FROM AUTHOR]

Summary: Some essential components of fleshy fruits are dependent on photosynthetic activity and carbohydrate metabolism. Nevertheless, the regulatory mechanisms linking chlorophyll and carbohydrate metabolism remain partially understood.Here, we uncovered the role of SlGRAS9 and SlZHD17 transcription factors in controlling chlorophyll and carbohydrate accumulation in tomato fruit. Knockout or knockdown of SlGRAS9 or SlZHD17 resulted in marked increase in chlorophyll content, reprogrammed chloroplast biogenesis and enhanced accumulation of starch and soluble sugars.Combined genome‐wide transcriptomic profiling and promoter‐binding experiments unveiled a complex mechanism in which the SlGRAS9/SlZHD17 regulatory module modulates the expression of chloroplast and sugar metabolism either via a sequential transcriptional cascade or through binding of both TFs to the same gene promoters, or, alternatively, via parallel pathways where each of the TFs act on different target genes. For instance, the regulation of SlAGPaseS1 and SlSUS1 is mediated by SlZHD17 whereas that of SlVI and SlGLK1 occurs only through SlGRAS9 without the intervention of SlZHD17. Both SlGRAS9 and SlZHD17 can also directly bind the promoter of SlPOR‐B to regulate its expression.Taken together, our findings uncover two important regulators acting synergistically to manipulate chlorophyll and carbohydrate accumulation and provide new potential breeding targets for improving fruit quality in fleshy fruits. [ABSTRACT FROM AUTHOR]

Summary: Soluble sugars, organic acids and volatiles are important components that determine unique fruit flavor and consumer preferences. However, the metabolic dynamics and underlying regulatory networks that modulate overall flavor formation during fruit development and ripening remain largely unknown for most fruit species.In this study, by integrating flavor‐associated metabolism and transcriptome data from 12 fruit developmental and ripening stages of Actinidia chinensis cv Hongyang, we generated a global map of changes in the flavor‐related metabolites throughout development and ripening of kiwifruit.Using this dataset, we constructed complex regulatory networks allowing to identify key structural genes and transcription factors that regulate the metabolism of soluble sugars, organic acids and important volatiles in kiwifruit. Moreover, our study revealed the regulatory mechanism involving key transcription factors regulating flavor metabolism. The modulation of flavor metabolism by the identified key transcription factors was confirmed in different kiwifruit species providing the proof of concept that our dataset provides a suitable tool for clarification of the regulatory factors controlling flavor biosynthetic pathways that have not been previously illuminated.Overall, in addition to providing new insight into the metabolic regulation of flavor during fruit development and ripening, the outcome of our study establishes a foundation for flavor improvement in kiwifruit. See also the Commentary on this article by Fernie & Alseekh, 233: 8–10. [ABSTRACT FROM AUTHOR]

Summary: Fruit formation comprises a series of developmental transitions among which the fruit set process is essential in determining crop yield. Yet, our understanding of the epigenetic landscape remodelling associated with the flower‐to‐fruit transition remains poor.We investigated the epigenetic and transcriptomic reprogramming underlying pollination‐dependent and auxin‐induced flower‐to‐fruit transitions in the tomato (Solanum lycopersicum) using combined genomewide transcriptomic profiling, global ChIP‐sequencing and whole genomic DNA bisulfite sequencing (WGBS).Variation in the expression of the overwhelming majority of genes was associated with change in histone mark distribution, whereas changes in DNA methylation concerned a minor fraction of differentially expressed genes. Reprogramming of genes involved in processes instrumental to fruit set correlated with their H3K9ac or H3K4me3 marking status but not with changes in cytosine methylation, indicating that histone posttranslational modifications rather than DNA methylation are associated with the remodelling of the epigenetic landscape underpinning the flower‐to‐fruit transition.Given the prominent role previously assigned to DNA methylation in reprogramming key genes of the transition to ripening, the outcome of the present study supports the idea that the two main developmental transitions in fleshy fruit and the underlying transcriptomic reprogramming are associated with different modes of epigenetic regulations. [ABSTRACT FROM AUTHOR]

Summary: RIPENING INHIBITOR (RIN)‐deficient fruits generated by CRISPR/Cas9 initiated partial ripening at a similar time to wild‐type (WT) fruits but only 10% WT concentrations of carotenoids and ethylene (ET) were synthesized. RIN‐deficient fruit never ripened completely, even when supplied with exogenous ET. The low amount of endogenous ET that they did produce was sufficient to enable ripening initiation and this could be suppressed by the ET perception inhibitor 1‐MCP.The reduced ET production by RIN‐deficient tomatoes was due to an inability to induce autocatalytic system‐2 ET synthesis, a characteristic feature of climacteric ripening. Production of volatiles and transcripts of key volatile biosynthetic genes also were greatly reduced in the absence of RIN.By contrast, the initial extent and rates of softening in the absence of RIN were similar to WT fruits, although detailed analysis showed that the expression of some cell wall‐modifying enzymes was delayed and others increased in the absence of RIN.These results support a model where RIN and ET, via ERFs, are required for full expression of ripening genes. Ethylene initiates ripening of mature green fruit, upregulates RIN expression and other changes, including system‐2 ET production. RIN, ET and other factors are required for completion of the full fruit‐ripening programme. [ABSTRACT FROM AUTHOR]

Summary: Ethylene is the main hormone controlling climacteric fruit ripening; however, the mechanisms underlying the developmental transition leading to the initiation of the ripening process remain elusive, although the presumed role of active hormone interplay has often been postulated.To unravel the putative role of auxin in the unripe‐to‐ripe transition, we investigated the dynamics of auxin activity in tomato fruit and addressed the physiological significance of Sl‐SAUR69, previously identified as a RIN target gene, using reverse genetics approaches.Auxin signalling undergoes dramatic decline at the onset of ripening in wild‐type fruit, but not in the nonripening rin mutant. Sl‐SAUR69 exhibits reduced expression in rin and its up‐regulation results in premature initiation of ripening, whereas its down‐regulation extends the time to ripening. Overexpression of Sl‐SAUR69 reduces proton pump activity and polar auxin transport, and ectopic expression in Arabidopsis alters auxin transporter abundance, further arguing for its active role in the regulation of auxin transport.The data support a model in which Sl‐SAUR69 represses auxin transport, thus generating auxin minima, which results in enhanced ethylene sensitivity. This defines a regulation loop, fed by ethylene and auxin as the main hormonal signals and by RIN and Sl‐SAUR69 as modulators of the balance between the two hormones. [ABSTRACT FROM AUTHOR]

• Plant growth and development is coordinated by complex networks of interacting hormones, and cross-talk between ethylene and auxin signaling is essential for a wide range of plant developmental processes. Nevertheless, the molecular links underlying the interaction between the two hormones remain poorly understood. • In order to decipher the cross-talk between the Ethylene Response Factor Sl-ERF.B3 and Sl- IAA27, mediating ethylene and auxin signaling, respectively, we combined reverse genetic approaches, physiological methods, transactivation experiments and electrophoretic mobility shift assays. • Sl-ERF.B3 is responsive to both ethylene and auxin and ectopic expression of its dominant repressor version (ERF.B3-SRDX) results in impaired sensitivity to auxin with phenotypes recalling those previously reported for Sl-IAA27 downregulated tomato lines. The expression of Sl-IAA27 is dramatically reduced in the ERF.B3-SRDX lines and Sl-ERF.B3 is shown to regulate the expression of Sl-IAA27 via direct binding to its promoter. • The data support a model in which the ethylene-responsive Sl-ERF.B3 integrates ethylene and auxin signaling via regulation of the expression of the auxin signaling component Sl- IAA27. The study uncovers a molecular mechanism that links ethylene and auxin signaling in tomato. [ABSTRACT FROM AUTHOR]

• Root colonization by arbuscular mycorrhizal (AM) fungi is a complex and finely tuned process. Previous studies have shown that, among other plant hormones, auxin plays a role in this process but the specific involvement of Aux/IAAs, the key regulators of auxin responses, is still unknown. • In this study, we addressed the role of the tomato Sl-IAA27 during AM symbiosis by using Sl-IAA27-RNAi and pSL-IAA27::GUS stable tomato lines. • The data show that Sl-IAA27 expression is up-regulated by the AM fungus and that silencing of Sl-IAA27 has a negative impact on AM colonization. Sl-IAA27-silencing resulted in down-regulation of three genes involved in strigolactone synthesis, NSP1, D27 and MAX1, and treatment of Sl-IAA27-silenced plants with the strigolactone analog GR24 complemented their mycorrhizal defect phenotype. • Overall, the study identified an Aux/IAA gene as a new component of the signaling pathway controlling AM fungal colonization in tomato. This gene is proposed to control strigolactone biosynthesis via the regulation of NSP1. [ABSTRACT FROM AUTHOR]

Fruit ripening involves a complex interplay between ethylene and ripening-associated transcriptional regulators. Ethylene Response Factors ( ERFs) are downstream components of ethylene signaling, known to regulate the expression of ethylene-responsive genes. Although fruit ripening is an ethylene-regulated process, the role of ERFs remains poorly understood., The role of Sl- ERF. B3 in tomato ( Solanum lycopersicum) fruit maturation and ripening is addressed here using a chimeric dominant repressor version ( ERF. B3- SRDX)., Over-expression of ERF. B3- SRDX results in a dramatic delay of the onset of ripening, enhanced climacteric ethylene production and fruit softening, and reduced pigment accumulation. Consistently, genes involved in ethylene biosynthesis and in softening are up-regulated and those of carotenoid biosynthesis are down-regulated. Moreover, the expression of ripening regulators, such as RIN, NOR, CNR and HB-1, is stimulated in ERF.B3- SRDX dominant repressor fruits and the expression pattern of a number of ERFs is severely altered., The data suggest the existence of a complex network enabling interconnection between ERF genes which may account for the pleiotropic alterations in fruit maturation and ripening. Overall, the study sheds new light on the role of Sl- ERF. B 3 in the transcriptional network controlling the ripening process and uncovers a means towards uncoupling some of the main ripening-associated processes. [ABSTRACT FROM AUTHOR]