Fruit ripening in tomato (Solanum lycopersicum) is a complicated development process affected by both endogenous hormonal and genetic regulators and external signals. Although the role of NOR, a member of the NAC domain family, in mediating tomato fruit ripening has been established, its underlying molecular mechanisms remain unclear. To explore further the role of NAC transcription factors in fruit ripening, we characterized a new tomato NAC domain protein, named SlNAC4, which shows high accumulation in sepal and at the onset of fruit ripening. Various stress treatments including wounding, NaCl, dehydration and low temperature significantly increased the expression of SlNAC4. Reduced expression of SlNAC4 by RNA interference (RNAi) in tomato resulted in delayed fruit ripening, suppressed Chl breakdown and decreased ethylene synthesis mediated mainly through reduced expression of ethylene biosynthesis genes of system-2, and reduced carotenoids by alteration of the carotenoid pathway flux. Transgenic tomato fruits also displayed significant down-regulation of multiple ripening-associated genes, indicating that SlNAC4 functions as a positive regulator of fruit ripening by affecting ethylene synthesis and carotenoid accumulation. Moreover, we also noted that SlNAC4 could not be induced by ethylene and may function upstream of the ripening regulator RIN and positively regulate its expression. Yeast two-hybrid assay further revealed that SlNAC4 could interact with both RIN and NOR protein. These results suggested that ethylene-dependent and -independent processes are regulated by SlNAC4 in the fruit ripening regulatory network.

box genes encode a highly conserved gene family of transcriptional factors that regulate numerous developmental processes in plants. In this study, a tomato (Solanum lycopersicum) MADS-box gene, SlMADS1, was cloned and its tissue-specific expression profile was analyzed. The real-time polymerase chain reaction results showed that SlMADS1 was highly expressed in sepals and fruits; its expression level was increased with the development of sepals, while the transcript of SlMADS1 decreased significantly in accordance with fruit ripening. To further explore the function of SlMADS1, an RNA interference (RNAi) expression vector targeting SlMADS1 was constructed and transformed into tomato plants. Shorter ripening time of fruit was observed in SlMADS1-silenced tomatoes. The accumulation of carotenoid and the expression of PHYTOENE SYNTHETASE1 were enhanced in RNAi fruits. Besides, ethylene biosynthetic genes, including 1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE1A, 1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE6, 1-AMINOCYCLOPROPANE-1-CARBOXYLATE OXIDASE1, and 1-AMINOCYCLOPROPANE-1-CARBOXYLATE OXIDASE3, and the ethylene-responsive genes E4 and E8, which were involved in fruit ripening, were also up-regulated in silenced plants. SlMADS1 RNAi fruits showed approximately 2-to 4-fold increases in ethylene production compared with the wild type. Furthermore, SlMADS1-silenced seedlings displayed shorter hypocotyls and were more sensitive to 1-aminocyclopropane-1-carboxylate than the wild type. Additionally, a yeast two-hybrid assay revealed a clear interaction between SlMADS1 and SlMADS-RIN. These results suggest that SlMADS1 plays an important role in fruit ripening as a repressive modulator.

The purple kale (Brassica Oleracea var. acephala f. tricolor) is a mutation in kales, giving the mutant phenotype of brilliant purple color in the interior. Total anthocyanin analysis showed that the amount of anthocyanins in the purple kale was up to 1.73 mg g(-1) while no anthocyanin was detected in the white kale. To elucidate the molecular mechanism of the anthocyanin biosynthesis in the purple kale, we analyzed the expression of structural genes and some transcription factors associated with anthocyanin biosynthesis in the purple cultivar "Red Dove" and the white cultivar "White Dove". The result showed that nearly all the anthocyanin biosynthetic genes showed higher expression levels in the purple cultivar than in the white cultivar, especially for DFR and ANS, they were barely detected in the white cultivar. Interestingly, the fact that a R2R3 MYB transcription factor named BoPAP1 was extremely up-regulated in the purple kale and induced by low temperature attracted our attention. Further sequence analysis showed that BoPAP1 shared high similarity with AtPAP1 and BoMYB1. In addition, the anthocyanin accumulation in the purple kale is strongly induced by the low temperature stress. The total anthocyanin contents in the purple kale under low temperature were about 50-fold higher than the plants grown in the greenhouse. The expression of anthocyanin biosynthetic genes C4H, F3H, DFR, ANS and UFGT were all enhanced under the low temperature. These evidences strongly suggest that BoPAP1 may play an important role in activating the anthocyanin structural genes for the abundant anthocyanin accumulation in the purple kale.

A novel member of the AP2/ERF transcription factor family, SlERF5, was identified from a tomato mature leaf cDNA library screen. The complete DNA sequence of SlERF5 encodes a putative 244-amino acid DNA-binding protein which most likely acts as a transcriptional regulator and is a member of the ethylene responsive factor (ERF) superfamily. Analysis of the deduced SlERF5 protein sequence showed that it contained an ERF domain and belonged to the class III group of ERFs proteins. Expression of SlERF5 was induced by abiotic stress, such as high salinity, drought, flooding, wounding and cold temperatures. Over-expression of SlERF5 in transgenic tomato plants resulted in high tolerance to drought and salt stress and increased levels of relative water content compared with wild-type plants. This study indicates that SlERF5 is mainly involved in the responses to abiotic stress in tomato.

Eggplant (Solanum melongena L.) is an edible fruit vegetable cultivated and consumed worldwide. The purple eggplant is more eye-catching and popular for the health-promoting anthocyanins contained in the fruit skin. Two kinds of anthocyanin were separated and identified from purple cultivar (Zi Chang) by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry. To investigate the molecular mechanisms of anthocyanin accumulation in eggplant, the transcripts of anthocyanin biosynthetic and regulatory genes were analyzed in the fruit skin and the flesh of the purple cultivar and the white cultivar (Bai Xue). Compared with the other tissues, SmMYB1 and all anthocyanin biosynthetic genes except PAL were dramatically upregulated in the fruit skin of the purple cultivar. Overexpression of SmMYB1 activated abundant anthocyanin accumulation in the regenerating shoots of eggplant. These results prove that transcriptional activation of SmMYB1 accounts for constitutive upregulation of most anthocyanin biosynthetic genes and the onset of anthocyanin biosynthesis in the purple cultivar.

Fusarium oxysporum is a devastating pathogen causing extensive yield losses in a variety of crops and development of sustainable, environmentally friendly methods to improve crop resistance is crucial. We have used Host-Delivered RNA interference (HD-RNAi) technology to partially silence three different genes (FOW2, FRP1, and OPR) in the hemi-biotrophic fungus F. oxysporum f. sp. conglutinans. Expression of double stranded RNA (dsRNA) molecules targeting fungal pathogen genes was achieved in a number of transgenic Arabidopsis lines. F. oxysporum infecting the transgenic lines displayed substantially reduced mRNA levels on all three targeted genes, with an average of 75, 83, and 72% reduction for FOW2, FRP1, and OPR, respectively. The silencing of pathogen genes had a clear positive effect on the ability of the transgenic lines to fight infection. All transgenic lines displayed enhanced resistance to F. oxysporum with delayed disease symptom development, especially FRP1 and OPR lines. Survival rates after fungal infection were higher in the transgenic lines compared to control wild type plants which consistently showed survival rates of 10%, with FOW2 lines showing 25% survival; FRP1 lines 30–50% survival and OPR between 45 and 70% survival. The down-regulation effect was specific for the targeted genes without unintended effects in related genes. In addition to producing resistant crops, HD-RNAi can provide a useful tool to rapidly screen candidate fungal pathogenicity genes without the need to produce fungal knockout mutants.

MADS-box family genes encode transcription factors that are involved in multiple developmental processes in plants, especially in floral organ specification, fruit development, and ripening. However, a comprehensive analysis of tomato MADS-box family genes, which is an important model plant to study flower fruit development and ripening, remains obscure. To gain insight into the MADS-box genes in tomato, 131 tomato MADS-box genes were identified. These genes could be divided into five groups (Mα, Mβ, Mγ, Mδ, and MIKC) and were found to be located on all 12 chromosomes. We further analyzed the phylogenetic relationships among Arabidopsis and tomato, as well as the protein motif structure and exon–intron organization, to better understand the tomato MADS-box gene family. Additionally, owing to the role of MADS-box genes in floral organ identification and fruit development, the constitutive expression patterns of MADS-box genes at different stages in tomato development were identified. We analyzed 15 tomato MADS-box genes involved in floral organ identification and five tomato MADS-box genes related to fruit development by qRT-PCR. Collectively, our study provides a comprehensive and systematic analysis of the tomato MADS-box genes and would be valuable for the further functional characterization of some important members of the MADS-box gene family.

MADS-domain proteins are important transcription factors involved in many biological processes of plants. In our study, a tomato MADS-box gene, SlFYFL, was isolated. SlFYFL is expressed in all tissues of tomato and significantly higher in mature leave, fruit of different stages, AZ (abscission zone) and sepal. Delayed leaf senescence and fruit ripening, increased storability and longer sepals were observed in 35S:FYFL tomato. The accumulation of carotenoid was reduced, and ethylene content, ethylene biosynthetic and responsive genes were down-regulated in 35S:FYFL fruits. Abscission zone (AZ) did not form normally and abscission zone development related genes were declined in AZs of 35S:FYFL plants. Yeast two-hybrid assay revealed that SlFYFL protein could interact with SlMADS-RIN, SlMADS1 and SlJOINTLESS, respectively. These results suggest that overexpression of SlFYFL regulate fruit ripening and development of AZ via interactions with the ripening and abscission zone-related MADS box proteins.