Héctor Gordon Núñez-Palenius

Melon Fruits: Genetic Diversity, Physiology, and Biotechnology Features

Among Cucurbitaceae, Cucumis melo is one of the most important cultivated cucurbits. They are grown primarily for their fruit, which generally have a sweet aromatic flavor, with great diversity and size (50 g to 15 kg), flesh color (orange, green, white, and pink), rind color (green, yellow, white, orange, red, and gray), form (round, flat, and elongated), and dimension (4 to 200 cm). C. melo can be broken down into seven distinct types based on the previously discussed variations in the species. The melon fruits can be either climacteric or nonclimacteric, and as such, fruit can adhere to the stem or have an abscission layer where they will fall from the plant naturally at maturity. Traditional plant breeding of melons has been done for 100 years wherein plants were primarily developed as open-pollinated cultivars. More recently, in the past 30 years, melon improvement has been done by more traditional hybridization techniques. An improvement in germplasm is relatively slow and is limited by a restricted gene pool. Strong sexual incompatibility at the interspecific and intergeneric levels has restricted rapid development of new cultivars with high levels of disease resistance, insect resistance, flavor, and sweetness. In order to increase the rate and diversity of new traits in melon it would be advantageous to introduce new genes needed to enhance both melon productivity and melon fruit quality. This requires plant tissue and plant transformation techniques to introduce new or foreign genes into C. melo germplasm. In order to achieve a successful commercial application from biotechnology, a competent plant regeneration system of in vitro cultures for melon is required. More than 40 in vitro melon regeneration programs have been reported; however, regeneration of the various melon types has been highly variable and in some cases impossible. The reasons for this are still unknown, but this plays a heavy negative role on trying to use plant transformation technology to improve melon germplasm. In vitro manipulation of melon is difficult; genotypic responses to the culture method (i.e., organogenesis, somatic embryogenesis, etc.) as well as conditions for environmental and hormonal requirements for plant growth and regeneration continue to be poorly understood for developing simple in vitro procedures to culture and transform all C. melo genotypes. In many cases, this has to be done on an individual line basis. The present paper describes the various research findings related to successful approaches to plant regeneration and transgenic transformation of C. melo. It also describes potential improvement of melon to improve fruit quality characteristics and postharvest handling. Despite more than 140 transgenic melon field trials in the United States in 1996, there are still no commercial transgenic melon cultivars on the market. This may be a combination of technical or performance factors, intellectual property rights concerns, and, most likely, a lack of public acceptance. Regardless, the future for improvement of melon germplasm is bright when considering the knowledge base for both techniques and gene pools potentially useable for melon improvement.

Molecular biology of capsaicinoid biosynthesis in chili pepper (Capsicum spp.)

Capsicum species produce fruits that synthesize and accumulate unique hot compounds known as capsaicinoids in placental tissues. The capsaicinoid biosynthetic pathway has been established, but the enzymes and genes participating in this process have not been extensively studied or characterized. Capsaicinoids are synthesized through the convergence of two biosynthetic pathways: the phenylpropanoid and the branched-chain fatty acid pathways, which provide the precursors phenylalanine, and valine or leucine, respectively. Capsaicinoid biosynthesis and accumulation is a genetically determined trait in chili pepper fruits as different cultivars or genotypes exhibit differences in pungency; furthermore, this characteristic is also developmentally and environmentally regulated. The establishment of cDNA libraries and comparative gene expression studies in pungent and non-pungent chili pepper fruits has identified candidate genes possibly involved in capsaicinoid biosynthesis. Genetic and molecular approaches have also contributed to the knowledge of this biosynthetic pathway; however, more studies are necessary for a better understanding of the regulatory process that accounts for different accumulation levels of capsaicinoids in chili pepper fruits.

Anthocyanin accumulation and expression analysis of biosynthesis-related genes during chili pepper fruit development

Chili pepper (Capsicum annuum L.) cv. Árbol and Uvilla fruits differing in anthocyanin contents were analyzed to characterize the accumulation patterns. The maximum accumulation of the aglycon delphinidin occurred 20 days postanthesis (DPA) with higher content in Uvilla than in Árbol fruits. Regarding the cDNA library, 9 186 cDNA clones were selected. The clones with high homology to genes concerning anthocyanin biosynthesis, such as encoding chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3′,5′-hydroxylase (F3′5′H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), UDP Glc-flavonoid 3-O-gluco-syl transferase (UFGT), and also those possibly involved in anthocyanin transport into the vacuoles, an anthocyanin permease (ANP) and a glutathione S-transferase (GST) were used for gene expression analysis. In general, the expression of all investigated genes was developmentally regulated in both Árbol and Uvilla. CHS and CHI transcripts were expressed at the maximal level at 10 DPA, and then consistently declined throughout fruit development. F3′5′H, DFR, UFGT and GST expression exhibited a positive correlation with anthocyanin accumulation, and the highest transcript levels were detected prior to or by the time of maximum anthocyanin accumulation, depending on the chili pepper type. Pericarp fruit tissues from cv. Tampiqueño 74, an anthocyanin non-accumulator, also showed CHS, CHI, F3H, ANS and ANP expression at some developmental stages.

Plant-based porcine reproductive and respiratory syndrome virus VLPs induce an immune response in mice.

Porcine reproductive and respiratory syndrome virus (PRRSV) significantly affects the swine industry worldwide. An efficient, protective vaccine is still lacking. Here, we report for the first time the generation and purification of PRRSV virus like particles (VLPs) by expressing GP5, M and N genes in Nicotiana silvestris plants. The particles were clearly visible by transmission electron microscopy (TEM) with a size of 60-70 nm. Hydrodynamic diameter of the particles was obtained and it was confirmed that the VLPs had the appropriate size for PRRS virions and that the VLPs were highly pure. By measuring the Z potential we described the electrophoretic mobility behavior of VLPs and the best conditions for stability of the VLPs were determined. The particles were immunogenic in mice. A western blot of purified particles allowed detection of three coexpressed genes. These VLPs may serve as a platform to develop efficient PRRSV vaccines.

Air Layering and Tiny-Air Layering Techniques for Mesquite [Prosopis laevigata (H. B. ex Willd.) Johnst. M. C.] Tree Propagation

Prosopis laevigata is commonly known in Mexico as mesquite, and it is mostly found in the Central Mexican States. Mesquite has been driven to scarcity because the local population has used it for different purposes. Therefore, efficient, inexpensive, and reliable propagation methods are an aim to preserve and increase the mesquite resources. Air layering (treatment applied to young 1–1.2 m-long and 1.0–1.5.0 cm-wide branches) and tiny-air layering (applied to young 25–30 cm-long and 0.3–0.5 cm-wide branches) were investigated as asexual mesquite propagation methods. IBA (100, 250, and 500 mg l−1); NAA (50, 100, and 250 mg l−1); IAA (100, 250, and 500 mg l−1); and 2,4-D (100 and 1000 mg l−1) were used for the air layering method, whereas for the tiny-air layering protocol IBA (0.1, 0.3, 1.0, 3.0, 5.0, and 10.0 mg l−1) alone or combined with Chrysal were utilized. The highest response (90%) of air layerings was obtained with 500 mg l−1 IBA, having an average number of 1,785 roots per layering. For the tiny-air layering method, the best treatment was 3.0 mg l−1 IBA + Chrysal, which induced 90% of rooting, with an average number of 31.8 roots per layering.

Muskmelon Embryo Rescue Techniques Using In Vitro Embryo Culture

Among the major cucurbit vegetables, melon (Cucumis melo) has one of the greatest polymorphic fruit types and botanical varieties. Some melon fruits have excellent aroma, variety of flesh colors, deeper flavor, and more juice compared to other cucurbits. Despite numerous available melon cultivars, some of them are exceedingly susceptible to several diseases. The genetic background carrying the genes for tolerance and/or resistance for those diseases is found in wild melon landraces. Unfortunately, the commercial melon varieties are not able to produce viable hybrids when crossed with their wild melon counterparts. Plant tissue culture techniques are needed to surpass those genetic barriers. In vitro melon embryo rescue has played a main role to obtain viable hybrids originated from commercial versus wild melon crosses. In this chapter, an efficient and simple embryo rescue melon protocol is thoroughly described.