Biology subjects

McNelly, R.

Publications and source records attributed to McNelly, R..

5 recordsLinked to original sources

bioRxiv2025

Targeting granule initiation and amyloplast structure to create giant starch granules in wheat

Starch granule size influences the functional, digestive, and processing qualities of starch, but its genetic control in plants is poorly understood. Here, we demonstrate that both space and substrate constraints limit starch granule size in wheat and provide an approach to achieve substantial increases in granule size. Wheat starch typically contains large A-type and small B-type granules. To increase A-type granule size, we explored the effect of mutations in the plastid division component PARALOG OF ARC 6 (PARC6), which increases amyloplast size and therefore the space available for granule growth, and in B-GRANULE CONTENT 1 (BGC1), which reduces the number of granule initiations and thus competition between growing granules for space and substrates. While parc6 and bgc1 single mutants had only modest increases in A-type granule size, the parc6 bgc1 double mutant produced striking giant granules that were more than double the size of typical A-type granules. The increase in granule size in parc6 bgc1 was reproducible in both the glasshouse and field, and had no detectable effect on plant growth, grain size and starch composition or content. We demonstrate that the size increase affects a range of functional properties, including viscosity and pasting temperature. Overall, by targeting both constraints, we created a new class of giant cereal starch that has not been previously observed in nature, with altered physicochemical properties that can be used in food and industrial applications. Significance statementWe provide a major advance in understanding the factors determining starch granule size in plants - a trait that strongly influences starch functionality. Starch granules from cereals are typically smaller than those of most root/tuber crops, rarely exceeding 30 {micro}m. We created a novel cereal starch in wheat that exceeds this size range. By simultaneously increasing amyloplast size and reducing granule initiations, we increased space for granule growth and reduced competition between growing granules for substrates. This resulted in a new class of cereal starch where nearly 50% of the starch volume were in granules greater than 30 {micro}m, and some exceeded 50 {micro}m. These giant granules had altered physicochemical properties that could find novel application in food and industry.

plant biology↗

bioRxiv2024

A curve fitting method for analysing starch granule size distributions in cereals

Background and ObjectivesThe size distribution of starch granules is an important factor determining functional and nutritional properties of starch. However, a simple, standardised method for their analysis is lacking. Here, we developed an approach for estimating granule size parameters using a Python script that fits curves to volumetric granule size distributions generated using a Coulter counter. FindingsThe bimodal size distribution of starch from most wheat and barley cultivars could be best described with a mixed distribution curve. A log-normal distribution was fitted to the small B-type granules, and a normal distribution was fitted to the large A-type granules, allowing estimation of their relative abundance and size parameters, despite their overlapping size distributions. However, the optimal fitting is altered in wheat mutants with large perturbations in B-type granule content. In maize and rice, which have unimodal granule size distributions, size parameters were calculated by fitting a single normal distribution. ConclusionsCurve fitting is an effective approach for estimating starch granule size parameters in diverse cereals, particularly the Triticeae with A- and B-type granules. Significance and noveltyWe provide new tools and guidelines for the quantitative analysis of granule size in cereals.

plant biology↗

bioRxiv2023

Modification of amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

Starch granule morphology is a major factor determining the functional and nutritional properties of starch. Here, we reveal amyloplast structure plays an important role in starch granule morphogenesis in wheat endosperm. Wheat amyloplasts contain large discoid A-type granules and small spherical B-type granules. We isolated a mutant in durum wheat defective in the plastid division protein PARC6, which had increased plastid size in both leaves and endosperm. Endosperm amyloplasts of the mutant contained more A- and B-type granules than those of the wild type. In mature grains, the mutant had larger A- and B-type granules than the wild type, and its A-type granules had a highly aberrant, lobed surface. This defect in granule morphology was already evident at early stages of grain development, when granule size was identical between the mutant and the wild type, and occurred without obvious alterations in starch polymer structure and composition. Plant growth and photosynthetic efficiency, as well as the size, number and starch content of grains, were not affected in the Ttparc6 mutants despite the large changes in plastid size. Interestingly, mutation of the PARC6 paralog, ARC6, in durum wheat did not increase plastid or starch granule size. We suggest this is because TtPARC6 can complement disrupted TtARC6 function by interacting with PDV2, the outer plastid envelope protein that typically interacts with ARC6 to promote plastid division. We propose that amyloplast compartment size and available stromal volume play important roles in determining starch granule size, shape and number per amyloplast.

plant biology↗

bioRxiv2022

A two-gene strategy increases the iron and zinc concentration of wheat flour and improves mineral bioaccesibility for human nutrition.

Dietary deficiencies of iron and zinc cause human malnutrition globally, which can be mitigated by biofortified staple crops. Conventional breeding approaches to increase grain mineral concentrations in wheat (Triticum aestivum L.) have had only limited success so far due to relatively low genetic variation. Here we demonstrate that a transgenic approach combining endosperm-specific expression of the wheat vacuolar iron transporter gene TaVIT2-D with constitutive expression of the rice nicotianamine synthase gene OsNAS2 has the potential to dramatically improve mineral micronutrient intake from wheat products. In two distinct bread wheat cultivars, we show that the VIT-NAS construct led to a two-fold increase in zinc to [~]50 {micro}g g-1 in wholemeal flour and a two-fold increase in both zinc and iron in hand-milled white flour. In highly pure, roller-milled white flour, the concentration of iron was enhanced three-fold to [~]25 {micro}g g-1. A greater than three-fold increase in the level of the natural plant metal chelator nicotianamine in the grain of VIT-NAS lines was associated with improved iron and zinc bioaccessibility in white flour. The growth of VIT-NAS plants in the greenhouse was indistinguishable from untransformed controls. We conclude that the effects of each gene cassette are additive in altering the total concentration and distribution of iron and zinc in wheat grains. This demonstrates the potential of a transgenic approach to enhance the nutritional quality of wheat well beyond what is possible by breeding approaches in order to alleviate dietary mineral deficiencies.

plant biology↗

bioRxiv2019

Sequencing smart: De novo sequencing and assembly approaches for non-model mammals.

BackgroundWhilst much sequencing effort has focused on key mammalian model organisms such as mouse and human, little is known about the correlation between genome sequencing techniques for non-model mammals and genome assembly quality. This is especially relevant to non-model mammals, where the samples to be sequenced are often degraded and low quality. A key aspect when planning a genome project is the choice of sequencing data to generate. This decision is driven by several factors, including the biological questions being asked, the quality of DNA available, and the availability of funds. Cutting-edge sequencing technologies now make it possible to achieve highly contiguous, chromosome-level genome assemblies, but relies on good quality high-molecular-weight DNA. The funds to generate and combining these data are often only available within large consortiums and sequencing initiatives, and are often not affordable for many independent research groups. For many researchers, value-for-money is a key factor when considering the generation of genomic sequencing data. Here we use a range of different genomic technologies generated from a roadkill European Polecat (Mustela putorius) to assess various assembly techniques on this low-quality sample. We evaluated different approaches for de novo assemblies and discuss their value in relation to biological analyses.\n\nResultsGenerally, assemblies containing more data types achieved better scores in our ranking system. However, when accounting for misassemblies, this was not always the case for Bionano and low-coverage 10x Genomics (for scaffolding only). We also find that the extra cost associated with combining multiple data types is not necessarily associated with better genome assemblies.\n\nConclusionsThe high degree of variability between each de novo assembly method (assessed from the seven key metrics) highlights the importance of carefully devising the sequencing strategy to be able to carry out the desired analysis. Adding more data to genome assemblies not always results in better assemblies so it is important to understand the nuances of genomic data integration explained here, in order to obtain cost-effective value-for-money when sequencing genomes.

genomics↗