Rafael Fernández-Muñoz

Uniform ripening Encodes a Golden 2-like Transcription Factor Regulating Tomato Fruit Chloroplast Development

Pretty or Sweet The grocery-store tomato that looks beautiful but tastes like tart cardboard arises from selection processes favoring phenotypes that make commercial production more reliable. Significant in that selection process was a mutation that reduced the mottled color variations of unripe green tomatoes, leaving them a uniform, pale, green. Powell et al. (p. 1711) analyzed the molecular biology of the mutation. The uniform ripening mutation turns out to disable a transcription factor called Golden 2-like (GLK2). GLK2 expression increases the fruits photosynthetic capacity, resulting in higher sugar content. Controlling when tomatoes turn from green to red requires knocking out the gene that adds flavor. Modern tomato (Solanum lycopersicum) varieties are bred for uniform ripening (u) light green fruit phenotypes to facilitate harvests of evenly ripened fruit. U encodes a Golden 2-like (GLK) transcription factor, SlGLK2, which determines chlorophyll accumulation and distribution in developing fruit. In tomato, two GLKs—SlGLK1 and SlGLK2—are expressed in leaves, but only SlGLK2 is expressed in fruit. Expressing GLKs increased the chlorophyll content of fruit, whereas SlGLK2 suppression recapitulated the u mutant phenotype. GLK overexpression enhanced fruit photosynthesis gene expression and chloroplast development, leading to elevated carbohydrates and carotenoids in ripe fruit. SlGLK2 influences photosynthesis in developing fruit, contributing to mature fruit characteristics and suggesting that selection of u inadvertently compromised ripe fruit quality in exchange for desirable production traits.

Synergistic Interaction Between Tomato chlorosis virus and Tomato spotted wilt virus Results in Breakdown of Resistance in Tomato

ABSTRACT Multiple viral infections frequently are found in single plants of cultivated and wild hosts in nature, with unpredictable pathological consequences. Synergistic reactions were observed in mixed infections in tomato plants doubly infected with the positive-sense and phloem-limited single-stranded RNA (ssRNA) crinivirus Tomato chlorosis virus (ToCV) and the negative-sense ssRNA tospovirus Tomato spotted wilt virus (TSWV). Synergism in a tomato cultivar susceptible to both viruses resulted in a rapid death of plants. A pronounced enhancement of ToCV accumulation mediated by TSWV co-infection was observed with no evident egress of ToCV from phloem tissues. No consistent alteration of TSWV accumulation was detected. More remarkable was the synergism observed in tomato cultivars which carry the Sw-5 resistance gene, which are resistant to TSWV. Pre-infection with ToCV resulted in susceptibility to TSWV, whereas co-inoculations did not. This suggested that a threshold level or a time lapse is needed for ToCV to interfere or downregulate the defense response in the TSWV-resistant plants.

Whitefly Resistance Traits Derived from the Wild Tomato Solanum pimpinellifolium Affect the Preference and Feeding Behavior of Bemisia tabaci and Reduce the Spread of Tomato yellow leaf curl virus

Breeding of tomato genotypes that limit whitefly (Bemisia tabaci) access and feeding might reduce the spread of Tomato yellow leaf curl virus (TYLCV), a begomovirus (genus Begomovirus, family Geminiviridae) that is the causal agent of tomato yellow leaf curl disease. TYLCV is restricted to the phloem and is transmitted in a persistent manner by B. tabaci. The tomato breeding line ABL 14-8 was developed by introgressing type IV leaf glandular trichomes and secretion of acylsucroses from the wild tomato Solanum pimpinellifolium accession TO-937 into the genetic background of the whitefly- and virus-susceptible tomato cultivar Moneymaker. Results of preference bioassays with ABL 14-8 versus Moneymaker indicated that presence of type IV glandular trichomes and the production of acylsucrose deterred the landing and settling of B. tabaci on ABL 14-8. Moreover, electrical penetration graph studies indicated that B. tabaci adults spent more time in nonprobing activities and showed a reduced ability to start probing. Such behavior resulted in a reduced ability to reach the phloem. The superficial type of resistance observed in ABL 14-8 against B. tabaci probing significantly reduced primary and secondary spread of TYLCV.

Inheritance of Resistance to Watermelon mosaic virus in Cucumis melo that Impairs Virus Accumulation, Symptom Expression, and Aphid Transmission

ABSTRACT The Cucumis melo accession TGR-1551 was found to be resistant to Watermelon mosaic virus (WMV, genus Potyvirus, family Potyviridae). The resistance resulted in a drastic and significant reduction of virus titer and infected plants were asymptomatic or exhibited mild disease symptoms. The same gene or closely linked genes restricted virus accumulation and ameliorated symptom expression. No effect was observed on virus accumulation in inoculated leaves, which suggested that the initial phases of infection were not affected. The resistance was effective against a range of WMV isolates from Spanish melon production areas. Using aphid inoculations, resistant plants showed a lower propensity for infection by WMV and for serving as virus sources for secondary spread once infected. Resistance was determined to be under recessive genetic control.

Increasing tomato fruit quality by enhancing fruit chloroplast function. A double-edged sword?

Fruits are generally regarded as photosynthate sinks as they rely on energy provided by sugars transported from leaves to carry out the highly demanding processes of development and ripening; eventually these imported photosynthates also contribute to the fruit organoleptic properties. Three recent reports have revealed, however, that transcriptional factors enhancing chloroplast development in fruit may result in higher contents not only of tomato fruit-specialized metabolites but also of sugars. In addition to suggesting new ways to improve fruit quality by fortifying fruit chloroplasts and plastids, these results prompted us to re-evaluate the importance of the contribution of chloroplasts/photosynthesis to fruit development and ripening.

In vitro germination of pepper pollen in liquid medium

Abstract A liquid medium containing 5–10% sucrose, 0.1 mM boric acid and 1 mM calcium chloride supported a germination percentage close to 50% and the best tube growth for in vitro germination of Capsicum annuum pollen (F1 hybrid ‘Latino’). The use of sucrose gave better results in terms of germination and/or tube growth than other sugars or polyethylene glycol. The germination of the pollen declined with time after flower opening. The optimized medium was used to study the effect of cold night temperature on pollen viability and the results were compared with those obtained by two staining methods (acetocarmine and fluorochromatic reaction). The results obtained with the improved medium for the in vitro pollen germination related more accurately with the number of seeds per fruit, at cold night temperature, than did the staining tests employed.

Kinetic studies of peptide bond formation. Effect of chloramphenicol

There might be an undetermined order in the interaction of the substrates with the ribosomes in the reaction of CACCA-Leu-Ac with puromycin to form Ac-Leu-puromycin and CACCA (‘fragment reaction’). Km 0°=6×10-4 M for the puromycin · ribosome interaction. Chloramphenicol totally blocks the ‘fragment reaction’ as a consequence of a single interaction with the ribosome of Kd 0°=2.2×10-6 M. The inhibition by chloramphenicol of the ‘fragment reaction’ is mixed competitive for puromycin.

[51] Ribosomal peptidyltransferase: Binding of inhibitors

Publisher Summary This chapter describes and emphasizes on two methods for the quantitative analysis of antibiotic-binding to ribosomes: equilibrium dialysis, and ethanol precipitation. The assays give estimates for the dissociation constant and number of available binding sites, and are suitable for correlation with resolved assays of the peptidyl transfer reaction and of substrate-binding at the peptidyltransferase center. The methods are applicable not only to a variety of labeled compounds that bind to the ribosome, but also to unlabeled compounds that compete with the labeled compounds for binding. The alcohol precipitation assay is intended primarily for the correlation of studies on the binding of inhibitors with studies on the peptidyl transfer reaction, but it is also useful for examination of competition between different compounds, and for routine assay of ribosome activities. The equilibrium dialysis assay is of more general applicability, and can be used in a wide range of conditions. Both methods are applicable to eukaryote as well as prokaryote ribosomes.

Binding of puromycin to E. coli ribosomes. Effects of puromycin analogues and peptide bond formation inhibitors

Abstract3H-puromycin binds to bacterial ribosomes, in the presence of ethanol, under the experimental conditions of the fragment reaction assay. The binding is feeble, takes place at 0°C, is partially inhibited by chloramphenicol and lincomycin and totally by sparsomycin. 3H-puromycin binding is hardly affected by the 3′ aminonucleoside of puromycin, is well inhibited by the L-Phenylalanine and L-Leucine analogues of puromycin and totally blocked by L-Phenylalanyl-adenosine.

Acylsucrose-Producing Tomato Plants Forces Bemisia tabaci to Shift Its Preferred Settling and Feeding Site

Background The whitefly Bemisia tabaci (Genn.) causes dramatic damage to plants by transmitting yield-limiting virus diseases. Previous studies proved that the tomato breeding line ABL 14-8 was resistant to B. tabaci, the vector of tomato yellow leaf curl disease (TYLCD). This resistance is based on the presence of type IV glandular trichomes and acylsucrose production. These trichomes deter settling and probing of B. tabaci in ABL 14-8, which reduces primary and secondary spread of TYLCD. Methodology/Principal Findings Whitefly settlement preference was evaluated on the adaxial and abaxial leaf surfaces of nearly-isogenic tomato lines with and without B. tabaci-resistance traits, ‘ABL 14-8 and Moneymaker’ respectively, under non-choice and free-choice conditions. In addition, the Electrical Penetration Graph technique was used to study probing and feeding activities of B. tabaci on the adaxial and abaxial leaf surfaces of the same genotypes. B. tabaci preferred to settle on the abaxial than on the adaxial surface of ‘Moneymaker’ leaves, whereas no such preference was observed on ABL 14-8 tomato plants at the ten-leaf growth stage. Furthermore, B. tabaci preferred to feed on the abaxial than on the adaxial leaf surface of ‘Moneymarker’ susceptible tomato plants as shown by a higher number of sustained phloem feeding ingestion events and a shorter time to reach the phloem. However, B. tabaci standard probing and feeding behavior patterns were altered in ABL 14-8 plants and whiteflies were unable to feed from the phloem and spent more time in non-probing activities when exposed to the abaxial leaf surface. Conclusions/Significance The distorted behavior of B. tabaci on ABL 14-8 protects tomato plants from the transmission of phloem-restricted viruses such as Tomato yellow leaf curl virus (TYLCV), and forces whiteflies to feed on the adaxial side of leaves where they feed less efficiently and become more vulnerable to natural enemies.