Quantitative changes in tRNA during ethylene induced ripening (ageing) of tomato fruits

Iso-accepting forms of tRNA^met, tRNA^leu, tRNA^lys, and tRNA^tyr were isolated from combined walls and septa of tomato fruits at 5 consecutive stages of ethylene induced ripening. Changes in the relative amount of some tRNA^leu and tRNA^lys were discerned 10hr after exposure to ethylene. Individual patterns of change for each of several iso-acceptor tRNAs were evident throughout the ripening sequence. Maximal changes were: tRNA^lys, ?66.3%; tRNA^leu, ?24.8%; and tRNA^met, +26.7%.     

Identification of an ETR1-homologue from mango fruit expressing during fruit ripening and wounding

We have isolated a mango (Mangifera indica L.) cDNA homologue of the ethylene receptor gene ETR-1, referred to as METR1, which codes for a polypeptide of 802 amino acids with a predicted molecular weight of 89 kDa. The amino acid sequence is highly homologous (over 80 percnt;) to ETRs from other fruits. Genomic Southern blot analysis indicates that two or more ETR homologues exist in mango. RNA blot analysis revealed that the level of METR1 mRNA in the mesocarp increased during fruit ripening. In addition, it was found that the METR1 mRNA increases transiently during wounding of the tissue. This is the first report of an ETR homologue showing an induction during fruit ripening and wounding.     

Overexpression of the persimmon abscisic acid β‐glucosidase gene (DkBG1) alters fruit ripening in transgenic tomato

β‐Glucosidases (BG) are present in many plant tissues. Among these, abscisic acid (ABA) β‐glucosidases are thought to take part in the adjustment of cellular ABA levels, however the role of ABA‐BG in fruits is still unclear. In this study, through RNA‐seq analysis of persimmon fruit, 10 full‐length DkBG genes were isolated and were all found to be expressed. In particular, DkBG1 was highly expressed in persimmon fruits with a maximum expression 95 days after full bloom (DAFD). We verified that, in vitro, DkBG1 protein can hydrolyze ABA‐glucose ester (ABA‐GE) to release free ABA. Compared with wild‐type, tomato plants that overexpressed DkBG1 significantly upregulated the expression of ABA receptor PYL3/7 genes and showed typical symptoms of ABA hypersensitivity in fruits. DkBG1 overexpression (DkBG1‐OE) accelerated fruit ripening onset by 3–4 days by increasing ABA levels at the pre‐breaker stage and induced early ethylene release compared with wild‐type fruits. DkBG1‐OE altered the expression of ripening regulator NON‐RIPENING (NOR) and its target genes; this in turn altered fruit quality traits such as coloration. Our results demonstrated that DkBG1 plays an important role in fruit ripening and quality by adjusting ABA levels via hydrolysis of ABA‐GE.     

A novel tomato F‐box protein,SlEBF3, is involved in tuning ethylene signaling during plant development and climacteric fruit ripening

Ethylene is instrumental to climacteric fruit ripening and EIN3 BINDING F‐BOX (EBF) proteins have been assigned a central role in mediating ethylene responses by regulating EIN3/EIL degradation in Arabidopsis. However, the role and mode of action of tomato EBFs in ethylene‐dependent processes like fruit ripening remains unclear. Two novel EBF genes, SlEBF3 and SlEBF4, were identified in the tomato genome, and SlEBF3 displayed a ripening‐associated expression pattern suggesting its potential involvement in controlling ethylene response during fruit ripening. SlEBF3 downregulated tomato lines failed to show obvious ripening‐related phenotypes likely due to functional redundancy among SlEBF family members. By contrast, SlEBF3 overexpression lines exhibited pleiotropic ethylene‐related alterations, including inhibition of fruit ripening, attenuated triple‐response and delayed petal abscission. Yeast‐two‐hybrid system and bimolecular fluorescence complementation approaches indicated that SlEBF3 interacts with all known tomato SlEIL proteins and, consistently, total SlEIL protein levels were decreased in SlEBF3 overexpression fruits, supporting the idea that the reduced ethylene sensitivity and defects in fruit ripening are due to the SlEBF3‐mediated degradation of EIL proteins. Moreover, SlEBF3 expression is regulated by EIL1 via a feedback loop, which supposes its role in tuning ethylene signaling and responses. Overall, the study reveals the role of a novel EBF tomato gene in climacteric ripening, thus providing a new target for modulating fleshy fruit ripening.     

The O‐methyltransferase gene MdoOMT1 is required for biosynthesis of methylated phenylpropenes in ripe apple fruit

Phenylpropenes, such as eugenol and trans‐anethole, are important aromatic compounds that determine flavour and aroma in many herbs and spices. Some apple varieties produce fruit with a highly desirable spicy/aromatic flavour that has been attributed to the production of estragole, a methylated phenylpropene. To elucidate the molecular basis for estragole production and its contribution to ripe apple flavour and aroma we characterised a segregating population from a Royal Gala (RG, estragole producer) × Granny Smith (GS, non‐producer) apple cross. Two quantitative trait loci (QTLs; accounting for 9.2 and 24.8% of the variation) on linkage group (LG) 1 and LG2 were identified that co‐located with seven candidate genes for phenylpropene O‐methyltransferases (MdoOMT1–7). Of these genes, only expression of MdoOMT1 on LG1 increased strongly with ethylene and could be correlated with increasing estragole production in ripening RG fruit. Transient over‐expression in tobacco showed that MdoOMT1 utilised a range of phenylpropene substrates and catalysed the conversion of chavicol to estragole. Royal Gala carried two alleles (MdoOMT1a, MdoOMT1b) whilst GS appeared to be homozygous for MdoOMT1b. MdoOMT1a showed a higher affinity and catalytic efficiency towards chavicol than MdoOMT1b, which could account for the phenotypic variation at the LG1 QTL. Multiple transgenic RG lines with reduced MdoOMT1 expression produced lower levels of methylated phenylpropenes, including estragole and methyleugenol. Differences in fruit aroma could be perceived in these fruit, compared with controls, by sensory analysis. Together these results indicate that MdoOMT1 is required for the production of methylated phenylpropenes in apple and that phenylpropenes including estragole may contribute to ripe apple fruit aroma.     

Changes in polar lipids during ripening and senescence of cherry tomato (Lycopersicon esculentum): Relation to climacteric and ethylene increases

The entire senescence period, including ripening, is characterized in cherry tomato ( Lycopersicon esculentum Mill. var. cerasiforme Alef.) by two successive changes in overall polar lipid content. The rise in respiration of the fruit in the climacteric phase is accompanied by a large increase in lipids, notably phospholipids, such as phosphatidylcholine and phosphatidic acid. This suggests the coexistence of anabolic and catabolic processes in this first period. At the degreening stage of the fruit, decreased levels of monogalactosyldiacylglycerol and the disappearance of trigalactosyldiacylglycerol may indicate some degradation of the chloroplast compartment. Following a respiratory upsurge, a sudden breakdown of total lipids occurs concomitantly with maximal ethylene production. This breakdown is essentially caused by a parallel decrease in the amounts of phosphatidylcholine, phosphatidylethanolamine, phosphatidic acid and also phosphatidylglycerol. However, in the cherry tomato, lipid peroxidation, evaluated by alteration of fatty acid distribution, seems insufficient to account for the ethylene peak.     

Daminozide inhibits ethylene production in apple fruit by blocking the conversion of methionine to aminocyclopropane-1-carboxylic acid (ACC)

At harvest, fruit from apple trees sprayed with daminozide (+daminozide) had lower levels of aminocyclopropane-1-carboxylic acid (ACC) and produced significantly lower amounts of ethylene than untreated (–daminozide) fruit. Flesh discs from the fruit of +daminozide and –daminozide trees were fed precursors of ethylene to determine how daminozide inhibits ethylene production. ACC was metabolized to ethylene regardless of treatment. Methionine (MET), however, was only converted to ethylene by –daminozide fruit, and only after the fruit had been maintained at 4 °C for 5 months. +Daminozide fruit failed to convert MET to ethylene at harvest, as well as after cold storage. When daminozide was added to the incubation media of flesh discs it did not inhibit ethylene production or the conversion of ACC to ethylene. The addition of daminozide did, however, inhibit the metabolism of exogenous MET to ethylene. Aminooxyacetate acid (AOA) blocked both the endogenous production of ethylene and that from MET feeds. Daminozide inhibits ethylene production by preventing the conversion of MET to ACC, but it does not appear to act as a simple competitive inhibitor of ACC synthase activity.Abbreviations ACC aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - AOA aminooxyacetic acid - CH cycloheximide - MET methionine - PUT putrescine Author for correspondence