How to make almonds palatable: The domesticated almond tree has been feeding humans for millennia. Derivation from the wild, bitter, and toxic almond required loss of the cyanogenic diglucoside amygdalin. Sánchez-Pérez et al. sequenced the almond genome and analyzed the genomic region responsible for this shift. The key change turned out to be a point mutation in a transcription factor that regulates production of P450 monooxygenases in the biosynthetic pathway for the toxic compound. Science , this issue p. 1095

Almond (Prunus dulcis) is the principal Prunus species in which the consumed and thus commercially important part of the fruit is the kernel. As a result of continued selection, the vast majority of almonds have a nonbitter kernel. However, in the field, there are trees carrying bitter kernels, which are toxic to humans and, consequently, need to be removed. The toxicity of bitter almonds is caused by the accumulation of the cyanogenic diglucoside amygdalin, which releases toxic hydrogen cyanide upon hydrolysis. In this study, we identified and characterized the enzymes involved in the amygdalin biosynthetic pathway: PdCYP79D16 and PdCYP71AN24 as the cytochrome P450 (CYP) enzymes catalyzing phenylalanine-to-mandelonitrile conversion, PdUGT94AF3 as an additional monoglucosyl transferase (UGT) catalyzing prunasin formation, and PdUGT94AF1 and PdUGT94AF2 as the two enzymes catalyzing amygdalin formation from prunasin. This was accomplished by constructing a sequence database containing UGTs known, or predicted, to catalyze a β(1→6)-O-glycosylation reaction and a Basic Local Alignment Search Tool search of the draft version of the almond genome versus these sequences. Functional characterization of candidate genes was achieved by transient expression in Nicotiana benthamiana. Reverse transcription quantitative polymerase chain reaction demonstrated that the expression of PdCYP79D16 and PdCYP71AN24 was not detectable or only reached minute levels in the sweet almond genotype during fruit development, while it was high and consistent in the bitter genotype. Therefore, the basis for the sweet kernel phenotype is a lack of expression of the genes encoding the two CYPs catalyzing the first steps in amygdalin biosynthesis.

Onion (Allium cepa L.) is the second most important vegetable crop worldwide and is widely appreciated for its health benefits. Despite its significant economic importance and its value as functional food, onion has been poorly investigated with respect to its genetic diversity. Herein, we surveyed the genetic variation in the “Acquaviva red onion” (ARO), a landrace with a century-old history of cultivation in a small town in the province of Bari (Apulia, Southern of Italy). A set of 11 microsatellite markers were used to explore the genetic variation in a germplasm collection consisting of 13 ARO populations and three common commercial types. Analyses of genetic structure with parametric and non-parametric methods highlighted that the ARO represents a well-defined gene pool, clearly distinct from the Tropea and Montoro landraces with which it is often mistaken. In order to provide a description of bulbs, usually used for fresh consumption, soluble solid content and pungency were evaluated, showing higher sweetness in the ARO with respect to the two above mentioned landraces. Overall, the present study is useful for the future valorization of the ARO, which could be promoted through quality labels which could contribute to limit commercial frauds and improve the income of smallholders.

Kale (Brassica oleracea L. var. acephala) is a widely appreciated vegetable with a century-old history of cultivation in Italy. The present study was addressed to the collection and characterization of kale germplasm traditionally cultivated in Apulia, Southern Italy, nowadays at risk of genetic erosion. In total, nineteen Apulian kale accessions were acquired. Genotyping by means of simple sequence repeat (SSR) DNA markers led to the identification of highly informative primer combinations and highlighted significant patterns of molecular variation among accessions. Consistently, significant differences were observed with respect to morpho-agronomic traits, including yield and harvesting time, and the content of bioactive compounds, namely total phenols, flavonoids, and anthocyanins, associated with antioxidant activity. Overall, this study led to the establishment of an ex situ collection of great importance to preserve endangered Apulian kale germplasm and to provide seed access to potential growers. Meanwhile, it offers a first characterization of Apulian kale, useful to promote its consumption and valorisation through breeding programmes.

Powdery mildew (PM) is a widespread fungal disease of plants in temperate climates, causing significant economic losses in agricultural settings. Specific homologs of the MLO gene family are PM susceptibility factors, as their loss-of function results in durable PM resistance (mlo resistance) in several plant species. The role of MLO susceptibility genes in plant-pathogen interactions is still elusive, however it is known that they are strongly upregulated following PM infection. In this study, we investigated the structure of 414 Putative Promoter Regions (PPRs) of MLO genes and highlighted motif and regulatory element patterns related to genomic relationships among species and phylogenetic distance among homologs. A TC box-like motif and a thymine-rich motif were found to be overrepresented in MLO genes transcriptionally upregulated upon infection with PM fungi. As proof of concept, we showed that the expression of a melon (Cucumis melo L.) gene enriched for the motifs above mentioned was strongly upregulated upon infection with the PM fungus Podosphaera xanthii. While identifying a candidate MLO susceptibility gene in melon, this study provides insight on the transcriptional control of MLO genes and indicates diagnostic features useful to identify MLO susceptibility genes across species affected by the PM disease.

The bitterness and toxicity of wild-type seeds of Prunoideae is due to the cyanogenic glucoside amygdalin. In cultivated almond (Prunus dulcis (Mill.) D.A. Webb), a dominant mutation at the Sk locus prevents amygdalin accumulation and thus results in edible sweet kernels. Here, we exploited sequence similarity and synteny between the genomes of almond and peach (Prunus persica (L.) Batsch) to identify cleaved amplified polymorphic sequence (CAPS) molecular markers linked to the Sk locus. A segregant F₁ population was used to map these markers on the Sk genomic region, together with Sk-linked simple sequence repeat (SSR) markers previously described. Molecular fingerprinting of a cultivar collection indicated the possibility to use CAPS polymorphisms identified in this study in breeding programs arising from different parental combinations. Overall, we highlight a set of codominant markers useful for early selection of sweet kernel genotypes, an aspect of primary importance in almond breeding. In addition, by showing collinearity between the physical map of peach and the genetic map of almond with respect to the Sk genomic region, we provide valuable information for further marker development and Sk positional cloning.