The transcript abundance of VviOMT1 was higher in the pulp than the skin . In addition, the transcript abundance of VviOMT1 decreased significantly with °Brix level in the pulp. There were no significant differences in the trancript abundance in the skin or pulp for VviOMT2, VviOMT3 or VviOMT4 . There was a high correlation of the transcript abundance of VviOMT1 in the pulp with 2-isobutyl-3-methoxypyrazine concentrations in the berries . The transcript abundance of VviOMT2, VviOMT3, or VviOMT4 in either skin or pulp was not correlated with IBMP concentrations . This is consistent with the suggestion that the pulp is the main contributor of IBMP in the berry. Our data indicated that VviOMT1 in the pulp may contribute to the IBMP concentration in these berries.Orthologs of RIN and SPL tomato transcription factors, which are known to be very important fruit ripening trancription factors, were at much higher transcript levels in the skin and decline with °Brix level . The transcript abundance of the VviNOR ortholog in grape was higher in the pulp and increased slightly to peak at 25 °Brix. In addition, the transcript abundance of VviRAP2.3, an inhibitor of ripening in tomato , decreased in the skin with a valley at 23.2 °Brix; it belongs to Cluster 4 of the AP2/ERF superfamily . Of particular interest was VviWRKY53 [UniProt: F6I6B1], which had a very similar transcript profile as VviERF6L1 . AtWRKY53 is a TF that promotes leaf senescence and is induced by hydrogen peroxide. This is the first report we know of implicating WRKY53 in fruit ripening .
AtERF4 induces AtWRKY53 and leaf senescence, so the interactions between WRKY and ERF TFs are complex. WRKY TFs bind to the WBOX elements in promoters and VviERF6L1 has a number of WBOX elements in its promoter . In addition, AtMEKK1 regulates AtWRKY53 and the transcript abundance of VviMEKK1 peaked at 23.2 °Brix in the skin as well. Interestingly, 25 liter plant pot the transcript abundance of both VviERF4 and VviERF8, whose orthologs in Arabidopsis promote leaf senescence, were at their highest level of transcript abundance at the lowest °Brix levels examined in this study .This study focused on the very late stages of the mature Cabernet Sauvignon berry when fruit flavors are known to develop. Cabernet Sauvignon is an important red wine cultivar, originating from the Bordeaux region of France. It is now grown in many countries. Wines made from Cabernet Sauvignon are dark red with flavors of dark fruit and berries. They also can contain herbaceous characters such as green bell pepper flavor that are particulary prevalent in underripe grapes. Grape flavor is complex consisting not only of many different fruit descriptors, but descriptors that are frequently made up of a complex mixture of aromatic compounds. For example, black currant flavor, in part, can be attributed to 1,8-cineole, 3-methyl-1-butanol, ethyl hexanoate, 2- methoxy-3-isopropylpyrazine, linalool, 4-terpineol, and β- damascenone and major components of raspberry flavor can be attributed to α- and β-ionone, α- and β- phellandrene, linalool, β-damascenone, geraniol, nerol and raspberry ketone. Some common volatile compounds found in the aroma profiles of these dark fruits and berries include benzaldehyde, 1-hexanol, 2-heptanol, hexyl acetate, β-ionone, β-damascenone, linalool, and α-pinen.
In a study of Cabernet Sauvignon grapes and wines in Australia, Cabernet Sauvignon berry aromas were associated with trans-geraniol and 2-pentyl furan and Cabernet Sauvignon flavor was associated with 3-hexenol, 2-heptanol, heptadienol and octanal. In another comprehensive study of 350 volatiles of Cabernet Sauvignon wines from all over Australia, the factors influencing sensory attributes were found to be complex ; in part, norisoprenoids and δ − and γ-lactones were associated with sweet and fruity characteristics and red berry and dried fruit aromas were correlated with ethyl and acetate esters. In Cabernet Sauvignon wines from the USA, sensory attributes were complex also and significantly affected by alcohol level of the wine. Linalool and hexyl acetate were postitively associated with berry aroma and IBMP was positively correlated with green bell pepper aroma. In France, β-damascenone was found to contribute to Cabernet Sauvignon wine aroma. Thus, flavor development in berries and wines is very complex, being affected by a large number of factors including genetics, chemistry, time and environment. In this paper we begin to examine the changes in transcript abundance that may contribute to flavor development. We show that the transcript abundance of many genes involved in fatty acid, carotenoid, isoprenoid and terpenoid metabolism was increased in the skin and peaked at the °Brix levels known to have the highest fruit flavors . Many of these are involved in the production of dark fruit flavors such as linalool synthases, carotenoid dioxygenases and lipoxygenases. These genes serve as good candidates for berry development and flavor markers during ripening. A broader range of studies from different cultivars, locations and environments are needed to determine a common set of genes involved in berry and flavor development. A similar study was conducted on the production of volatile aromas in Cabernet Sauvignon berries across many developmental stages, including a detailed analysis of the °Brix levels that was surveyed in this study. They found that the production of alcohol volatiles from the lipoxygenase pathway dominated in the later stages of berry ripening and suggested that the activity of alcohol dehydrogenases also could play an important role.
The abundance of the transcript of VviOMT1 decreased in the pulp with increasing °Brix level and was correlated with IBMP concentrations in the late stages of berry development in this study. Both OMT and OMT3 have been shown to synthesize IBMP. Furthermore, the transcript abundance of each gene has been correlated with IBMP concentration, but the transcript abundance of each gene cannot fully account for the total IBMP present in all genotypes and conditions . OMT3 was found to be the major genetic determinant for this trait in two independent studies. Nevertheless, it is possible that OMT1 may contribute to the IBMP concentration, because OMT1 can synthesize IBMP and it is located at the edge of a QTL significantly contributing to this trait . Furthermore, the majority of IBHP , the precursor for the OMT1 and OMT3 biosynthesis of IBMP, is produced in the pulp of the berry complicating the factors that influence IBMP concentration. Our results raise questions that require additional research to clarify this relationship of transcript abundance to IBMP concentration, including determination of the rates of biosynthesis and catabolism, enzyme activities, volatilization of IBMP from the berry, as well as the concentrations of substrates for the enzymes involved. There are a number of other transcriptomic ripening studies in grapes and other fruit species. Many of these have compared broad developmental stages with partial genome microarrays. One study compared transcriptomic responses of the lates stages of ripening of whole berries of Chardonnay. This study used a different microarray platform with only about half of the genome represented on the array. In this study, 12 genes were found to be differentially expressed in each of the 3 different stages investigated. There were approximately another 50 genes that were differentially expressed at one stage versus another. Several genes were proposed as good candidates for markers of ripeness and these were also examined in Cabernet Sauvignon berries using qPCR. Several of these candidate genes are consistent with our results in the present study. They include CCD4a , a late embryogenesis abundant protein , a dirigent-like protein , and an S-adenosyl-L-methionine:salicylic acid carboxyl methyltransferase . Of these, the transcript expression of SAMT was found to be temperature insensitive. Like the previous study, the present study focused on very close stages in the mature berry when fruit flavors are known to develop. In contrast to the previous study on Chardonnay [86], there were massive changes in the transcript abundance in hundreds of GO categories over this narrow window of ripening. This may in part be due to using six biological replicates rather than the standard three, which probably improved the detection of significantly changing transcripts. In addition, we used a different threshold level for statistical significance and an improved microarray platform, black plastic plant pots which was able to detect double the number of transcripts. In the present study, many differences were found between the skin and the pulp, °Brix levels and the interaction of tissue and °Brix. Important fruit ripening processes were affected including ethylene signaling, senescence, volatile aroma production, lipid metabolism and cell wall softening. These data indicate that fruit ripening in the late stages of maturity is a very dynamic and active process.Ethylene is involved in climacteric fruit ripening with a CO2 burst preceding the rise in ethylene. In tomato, this occurs at the time the seeds become mature in the mature green fruit stage.
At this stage, tomato fruits become sensitive to ethyene and can continue through the ripening stage. Prior to the mature breaker stage, ethylene cannot promote tomato ripening to full ripeness. In non-climacteric fruit, there is no respiratory burst of CO2 and the ripening of most non-climacteric fruits was thought not to respond significantly to an extra application of ethylene. However, recently some non-climacteric fruit such as strawberry, bell pepper and grape have been found to produce a small amount of ethylene and appear to have responses to ethylene at certain stages. In the study of grapes, this peak was observed just before the start of veraison, followed by decreases in ethylene concentrations for several weeks afterwards; the late mature stages of ripening were not examined. Ethylene action is dependent upon ethylene concentration and ethylene sensitivity or signaling. In this study, there were clear and significant changes in transcript abundance of genes involved in ethylene signaling and biosynthesis in the late stages of berry ripening. Seeds become fully mature at this time . Perhaps there is a signal from the seeds when they become mature that allows the fruit to ripen and senesce? Perhaps small amounts of ethylene are produced or there is a change in sensitivity to ethylene? Seymour et al. suggested the response of EIN3 might be a common signaling mechanism for both climacteric and non-climacteric fruit. The responses of VviEIN3 in this study and in a pepper fruit ripening study are consistent with this hypothesis. In addition, the transcript abundance of VviEIN3 in grape is very responsive to ethylene and the ethylene inhibitor, MCP. There are many other factors other than fruit development that can influence ethylene signaling. Could chilling of the fruit or other aspects of the processing of the grapes influence these responses? Could there be some influence of other abiotic or biotic stresses? These are questions that can only be addressed in future studies with additional experiments that are designed to answer these questions.The strawberry , a member of the rose family, is not really a berry, but an achene or “false” fruit . A strawberry consists of many tiny individual fruits embedded in a fleshy scarlet receptacle. The brownish or whitish specks, commonly considered seeds, are the true fruits, known as achenes. Each achene surrounds a tiny seed. Strawberries are also an excellent source of vitamin C, a good source of folate and potassium, and are relatively low in calories . The strawberry is native to temperate regions around the world, including parts of North America. California grows approximately 83 percent of the nation’s strawberries that are marketed as fresh or frozen fruit. Strawberries are grown on over 25,000 acres in California, each producing an average of 21 tons of strawberries, seven times the national average. Strawberries are grown in five regions of California: San Diego, Orange County, Oxnard, Santa Maria, and Watsonville/Salinas. The California strawberry season extends from January through November along the California coast, with its peak in April, May, and June, when all five districts produce berries at once. Florida produces strawberries in the winter months , and additional berries are imported from Mexico during this time. The most common commercial varieties in California are the Camarosa, Diamonte, Chandler, and Selva. Proprietary and other varieties, representing about 32 percent of acreage, are bred and grown for individual shipping companies, and are not available to the public.The optimum storage temperature for strawberries in the home is 32° to 36°F . The optimum humidity for storage of berries to prevent water loss and shriveling is 90 to 95 percent. Store the fruit in the crisper drawer of your refrigerator. Keep strawberries packaged in closed plastic clamshell containers or place fruit in a partially opened plastic bag to maintain high humidity. Do not wash berries until just before eating or preserving. Washing will add moisture and will cause the berries to spoil more rapidly.