Diversity of Global Rice Markets and the Science Required for Consumer-Targeted Rice Breeding

With the ever-increasing global demand for high quality rice in both local production regions and with Western consumers, we have a strong desire to understand better the importance of the different traits that make up the quality of the rice grain and obtain a full picture of rice quality demographics. Rice is by no means a ‘one size fits all’ crop. Regional preferences are not only striking, they drive the market and hence are of major economic importance in any rice breeding / improvement strategy. In this analysis, we have engaged local experts across the world to perform a full assessment of all the major rice quality trait characteristics and importantly, to determine how these are combined in the most preferred varieties for each of their regions. Physical as well as biochemical characteristics have been monitored and this has resulted in the identification of no less than 18 quality trait combinations. This complexity immediately reveals the extent of the specificity of consumer preference. Nevertheless, further assessment of these combinations at the variety level reveals that several groups still comprise varieties which consumers can readily identify as being different. This emphasises the shortcomings in the current tools we have available to assess rice quality and raises the issue of how we might correct for this in the future. Only with additional tools and research will we be able to define directed strategies for rice breeding which are able to combine important agronomic features with the demands of local consumers for specific quality attributes and hence, design new, improved crop varieties which will be awarded success in the global market

A single nucleotide polymorphism in the Waxy gene explains a significant component of gel consistency

Gel consistency (GC) is a standard assay used in rice improvement programmes to determine whether rice cultivars/breeding lines of high amylose content are soft or firm textured when cooked. In this study, we show that sequence variation in exon 10 of the Waxy (Wx) gene associates with GC using RILs derived from parents with high amylose content that differ in GC. The association was validated using a diverse set of traditional varieties, selected on the basis of amylose content, from the generation challenge programme. Structural investigations to explain how the mutation leads to differences in GC showed a strong association between GC and the proportion of amylose that leaches. It was shown that cooked rices of hard GC do not change in hardness over 24 h, whereas rices of soft GC retrograde significantly over 24 h. This leads to the conclusion that the mutation on exon 10 of the Wx gene affects the proportion of amylose bound to amylopectin and the proportion able to leach, and these structural differences alter the composition of the gel, which affects the amount of time the gel takes to reach a final hardness. The SNP described here completes the set of markers required to genotype for the current traits of cooking quality, but selecting the allele for soft texture has the negative result of also selecting for retrogradation potential

A genomics and multi-platform metabolomics approach to identify new traits of rice quality in traditional and improved varieties

Using a novel approach combining four complementary metabolomic and mineral platforms with genome-wide genotyping at 1536 single nucleotide polymorphism (SNP) loci, we have investigated the extent of biochemical and genetic diversity in three commercially-relevant waxy rice cultivars important to food production in the Lao People’s Democratic Republic (PDR). Following cultivation with different nitrogen fertiliser regimes, multiple metabolomic data sets, including minerals, were produced and analysed using multivariate statistical methods to reveal the degree of similarity between the genotypes and to identify discriminatory compounds supported by multiple technology platforms. Results revealed little effect of nitrogen supply on metabolites related to quality, despite known yield differences. All platforms revealed unique metabolic signatures for each variety and many discriminatory compounds could be identified as being relevant to consumers in terms of nutritional value and taste or flavour. For each platform, metabolomic diversity was highly associated with genetic distance between the varieties. This study demonstrates that multiple metabolomic platforms have potential as phenotyping tools to assist breeders in their quest to combine key yield and quality characteristics. This better enables rice improvement programs to meet different consumer and farmer needs, and to address food security in rice-consuming countries

Proline Metabolism and Its Functions in Development and Stress Tolerance

Proline takes an exceptional place among the proteinogenic amino acids by its specific accumulation in pollen and in response to multiple types of stress. Despite the more than 50 years of research, the biochemical pathways of proline biosynthesis and degradation still await their complete characterization in plants. Also, the molecular and physiological functions of proline metabolism in plant development and defense against stress are not yet fully understood. This chapter focuses on the current knowledge about the biochemical pathways of proline metabolism in plants, on its tissue-specific regulation and subcellular compartmentation, and on still open questions. Furthermore, we will summarize what is known about the influence of proline metabolism on plant development under optimal growth conditions and how it may support continued development despite the impact of stress. The cognate chapter “Regulation of Proline Accumulation and its molecular and physiological Functions in Stress Defense” will focus on the possible beneficial functions of proline metabolism and accumulation in the defense response against diverse stresses. With these two cohesive chapters, we aim to provide a comprehensive picture of the current knowledge and the open research questions in proline-dependent stress defense