Research on the genetic control of flowering in potato set to blossom - The control of flowering in potato

‘Hello, just inspecting my spuds and spotted this fruit growing on a stem. It’s dark green and has a stalk attached. Anyone know what it might be?’ This was a question submitted by a gardener to an online discussion forum (Gardener’s World, 2014), and it is not unusual for gardeners to ask why their potato plants have flowers or berries (often described as small green tomatoes) on them (Fig. 1). The common misconception that potatoes do not flower or produce seeds arises, of course, because potatoes reproduce vegetatively as well as sexually, and growers plant ‘seed’ potatoes (pieces of tuber) rather than true seeds

Reducing the risk of acrylamide and other processing contaminant formation in wheat products

Wheat is a staple crop, consumed worldwide as a major source of starch and protein. Global intake of wheat has increased in recent years and overall wheat is considered to be a healthy food, particularly when products are made from whole grains. However, wheat is almost invariably processed before it is consumed, usually via baking and/or toasting, and this can lead to the formation of toxic processing contaminants, including acrylamide, 5-hydroxymethylfurfural (HMF) and polycyclic aromatic hydrocarbons (PAHs). Acrylamide is principally formed from free (soluble, non-protein) asparagine and reducing sugars (glucose, fructose and maltose) within the Maillard reaction and is classified as a Group 2A carcinogen (probably carcinogenic to humans). It also has neurotoxic and developmental effects at high doses. HMF is also generated within the Maillard reaction but can also be formed via the dehydration of fructose or caramelisation. It is frequently found in bread, biscuits, cookies, and cakes. Its molecular structure points to genotoxicity and carcinogenic risks. PAHs are a large class of chemical compounds, many of which are genotoxic, mutagenic, teratogenic and carcinogenic. They are mostly formed during frying, baking and grilling due to incomplete combustion of organic matter. Production of these processing contaminants can be reduced with changes in recipe and processing parameters, along with effective quality control measures. However, in the case of acrylamide and HMF their formation is also highly dependent on the concentrations of precursors in the grain. Here we review the synthesis of these contaminants, factors impacting their production and the mitigation measures that can be taken to reduce their formation in wheat products, focussing on the role of genetics and agronomy. We also review the risk management measures adopted by food safety authorities around the world

Cereal asparagine synthetase genes

Asparagine synthetase catalyses the transfer of an amino group from glutamine to aspartate to form glutamate and asparagine. The accumulation of free (non-protein) asparagine in crops has implications for food safety because free asparagine is the precursor for acrylamide, a carcinogenic contaminant that forms during high-temperature cooking and processing. Here we review publicly-available genome data for asparagine synthetase genes from species of the Pooideae subfamily, including bread wheat and related wheat species (Triticum and Aegilops spp.), barley (Hordeum vulgare) and rye (Secale cereale) of the Triticeae tribe. Also from the Pooideae subfamily: brachypodium (Brachypodium dystachion) of the Brachypodiae tribe. More diverse species are also included, comprising sorghum (Sorghum bicolor) and maize (Zea mays) of the Panicoideae subfamily, and rice (Oryza sativa) of the Ehrhartoideae subfamily. The asparagine synthetase gene families of the Triticeae species each comprise five genes per genome, with the genes assigned to four groups: 1, 2, 3 (subdivided into 3.1 and 3.2) and 4. Each species has a single gene per genome in each group, except that some bread wheat varieties (genomes AABBDD) and emmer wheat (Triticum dicoccoides; genomes AABB) lack a group 2 gene in the B genome. This raises questions about the ancestry of cultivated pasta wheat and the B genome donor of bread wheat, suggesting that the hybridisation event that gave rise to hexaploid bread wheat occurred more than once. In phylogenetic analyses, genes from the other species cluster with the Triticeae genes, but brachypodium, sorghum and maize lack a group 2 gene, while rice has only two genes, one group 3 and one group 4. This means that TaASN2, the most highly expressed asparagine synthetase gene in wheat grain, has no equivalent in maize, rice, sorghum or brachypodium. An evolutionary pathway is proposed in which a series of gene duplications gave rise to the five genes found in modern Triticeae species

Epigenetic switch reveals CRISPR/Cas9 response to cytosine methylation in plants: Comment

Commentary on Přibylová et al. (2022). 235 p 2285-2299 Genome editing techniques, such as the CRISPR/Cas9 system, offer a game-changing opportunity for crop improvement by enabling precise modifications to be made at targeted genomic loci. The CRISPR/Cas9 system has been employed successfully in many plant species; however, in order to use the system to its full potential, it is important to understand precisely how it functions and the factors that may limit its effectiveness. The mechanistic details of Cas9-induced double-strand breaks (DSBs), which underpin the mutational ability of the system, have been well described. It is also known that the efficiency of editing varies for different target sequences. However, the impact of epigenetic modifications on CRISPR/Cas9 efficacy and subsequent DNA repair is poorly understood, especially in plants. Epigenetic modifications affect gene regulation and genome stability. As such, the epigenetic status of an editing target site may influence the frequency of CRISPR/Cas9-induced mutations, for example by affecting how well Cas9 binds and cuts, or the efficiency and accuracy of DNA repair mechanisms. Genome-wide analyses have shown the efficiency of CRISPR/Cas9 editing to be lower for heterochromatin than euchromatin (Daer et al., 2017), although this is still contested (Kallimasioti-Pazi et al., 2018). However, comparisons of editing efficiencies between heterochromatin and euchromatin have involved the analysis of two or more loci, and different target loci vary in more than just their epigenetic status. In this issue of New Phytologist, Přibylová et al. (2022) investigate the effect of cytosine methylation on the generation of CRISPR/Cas9-induced mutations at multiple target sites within the same locus in Nicotiana benthamiana, using a virus-based epigenetic switch. This epigenetic switch allows for the conversion of the chromatin state of the target locus and so can be used to shed light on how cytosine methylation affects the frequency and outcome of CRISPR/Cas9 induced editing at a single site. The authors also highlighted the important role of single-nucleotide microhomology-mediated DNA repair in genome editing

The Maillard reaction in food processing and cooking

The Maillard reaction is one of the most important in the food industry and home cooking, being largely responsible for the colour, flavour, aroma and texture of some of our favourite foods. However, it also results in the formation of undesirable products, including the neurotoxin and probable carcinogen, acrylamide. The food industry is grappling with the task of reducing acrylamide levels in its products while retaining the characteristics that consumers want and expect

Vulnerability of European wheat to extreme heat and drought around flowering under future climate

Identifying the future threats to crop yields from climate change is vital to underpin the continuous production increases needed for global food security. In the present study, the vulnerability of European wheat yield to heat and drought stresses around flowering under climate change was assessed by estimating the 95-percentiles of two indices at flowering under rain-fed conditions: the heat stress index (HSI95) and the drought stress index (DSI95). These two indices represent the relative yield losses due heat stress or drought stress around flowering that could be expected to occur once every 20 years on average. The Sirius wheat model was run under the predicted 2050-climate at 13 selected sites, representing the major wheat-growing regions in Europe. A total of 19 global climate models (GCMs) from the CMIP5 ensemble were used to construct local-scale climate scenarios for 2050 (RCP8.5) by downscaling GCMs climate projections with the LARS-WG weather generator. The mean DSI95 due to extreme drought around flowering under the baseline climate (1981–2010) was large over Europe (DSI95 ∼ 0.28), with wide site variation (DSI95 ∼ 0.0–0.51). A reduction of 12% in the DSI95 was predicted under the 2050-climate; however, vulnerability due to extreme drought around flowering would remain a major constraint to wheat yield (DSI95 ∼ 0–0.57). In contrast, HSI95 under the baseline climate was very small over Europe (HSI95 ∼ 0.0–0.11), but was predicted to increase by 79% (HSI95 ∼ 0.0–0.23) under the 2050-climate, categorising extreme heat stress around flowering as an emergent threat to European wheat production. The development of wheat varieties that are tolerant to drought and heat stresses around flowering, is required, if climate change is not to result in a reduction of wheat yield potential under the future climate in Europe

Real-Time Quantitative PCR - Primer Design, Reference Gene Selection, Calculations and Statistics

Real-time quantitative PCR is a technique that can measure the content of the target nucleic acid sequence of interest in a given sample. It is mainly divided into absolute and relative quantitative methods. The relative quantification is mainly used in gene expressions for functional genomic and transcriptome studies. However, to use this technology accurately, there are some key points to master. First, specific primers need to be designed to ensure amplification of the gene of interest (GOI). Second, the appropriate reference gene or reference gene combination has to be selected. Finally, scientific gene expression level calculations and statistics are required to obtain accurate results. Therefore, this work proposes a workflow for relative quantitative PCR and introduces the relevant points so that beginners can better understand and use this technology

The sulphur response in wheat and its implications for acrylamide formation and food safety

Free (soluble, non-protein) asparagine concentration can increase many-fold in wheat grain in response to sulphur deficiency. This exacerbates a major food safety and regulatory compliance problem for the food industry because free asparagine may be converted to the carcinogenic contaminant, acrylamide, during baking and processing. Here we describe the predominant route for the conversion of asparagine to acrylamide in the Maillard reaction. The effect of sulphur deficiency and its interaction with nitrogen availability is reviewed, and we reiterate our advice that sulphur should be applied to wheat being grown for human consumption at a rate of 20 kg per hectare. We describe the genetic control of free asparagine accumulation, including genes that encode metabolic enzymes (asparagine synthetase, glutamine synthetase, glutamate synthetase and asparaginase), regulatory protein kinases (SnRK1 and GCN2) and bZIP transcription factors, and how this genetic control responds to sulphur, highlighting the importance of asparagine synthetase-2 (ASN2) expression in the embryo. We show that expression of glutamate-cysteine ligase is reduced in response to sulphur deficiency, probably compromising glutathione synthesis. Finally, we describe unexpected effects of sulphur deficiency on carbon metabolism in the endosperm, with large increases in expression of sucrose synthase-2 (SuSy2) and starch synthases