Fertilizer Deep Placement Significantly Affected Yield, Rice Quality, 2-AP Biosynthesis and Physiological Characteristics of the Fragrant Rice Cultivars

The management of fertilizers in a context of climate change and the preservation of the environment is strongly related to the regulation and accumulation of 2-acetyl-1-pyrroline (2AP) in fragrant rice. However, the feasibility of such management strategies in terms of enhancing the accumulation of 2AP has not yet been explored in aromatic cultivars. Here, we investigated the impact of the application of two fertilizers at three depth (surface, 5 cm and 10 cm) levels of placements to improve the aromatic rice quality, including such aspects as the 2AP content-, protein-, amylose- and yield-related traits. For this purpose, two known rice cultivars, Basmati 385 (B-385) and Yunjingyou (YJY), were grown in pots during 2019 and 2020 under fluctuating climates. The deep application of fertilizer at 10 cm significantly affected the 2AP content with such values as 127.53 μg kg−1 and 111.91 μg kg−1 obtained for Fragrant Fertilizer (FF) and Urea in B-385 cultivar, and 126.5 μg kg−1 and 114.24 μg kg−1 being observed for FF and Urea in YJY, respectively, during 2019. In addition, values of 108.41 μg kg−1 and 117.35 μg kg−1 were recorded for FF and Urea in B-385, while 125.91-μg kg−1 and 90.71-μg kg−1 were measured for FF and Urea in YJY, respectively, during 2020. Similarly, B-385 had better 2AP content and yield-related traits, as well as amylose content and cooked rice elongation, as compared to the YJY rice cultivar. The 2AP accumulation and its related biochemical parameters, and their relationships in different plant tissues at different growth stages under FF and Urea treatments, were also improved. Further, the 2AP content and the P5C activity demonstrated strong correlations during the grain filling periods in both fragrant rice cultivars. In conclusion, our findings have the potential to provide useful information to farmers and agriculture extension workers in terms of the saving of fertilizers and the improvement of rice grain quality under fluctuating climate conditions.

DEGENERATED LEMMA (DEL) Is a New Allele of OsRDR6 That Regulates Lemma Development and Affects Rice Grain Yield

The lemma and palea are floral organ structures unique to grasses, and their development affects grain size. However, information on the molecular mechanism of lemma development is limited. In this study, we investigated a rice spikelet mutant, degenerated lemma (del), which developed florets with a slightly degenerated or rod-like lemma. The results indicate that the mutation of the DEL gene interfered with lemma development. In addition, del also showed a significant reduction in grain length and width, seed setting rate, and 1000-grain weight, which led to a reduction in yield. The results indicate that the mutation of the DEL gene further affects rice grain yield. Map-based cloning shows a single-nucleotide substitution from T to A within Os01g0527600/DEL, causing an amino acid mutation of Leu-34 to His-34 in the del mutant. DEL is an allele of OsRDR6, encoding the RNA-dependent RNA polymerase 6, and is highly expressed in the spikelet. RT-qPCR results show that the expression of some floral organ identity genes was changed, which indicates that the DEL gene regulates lemma development by modulating the expression of these genes. The present results suggest that DEL plays an important role in lemma development and rice grain yield.

Metabolic Disturbance Induced by the Embryo Contributes to the Formation of Chalky Endosperm of a Notched-Belly Rice Mutant

Grain chalkiness is a key quality trait of the rice grain, whereas its underlying mechanism is still not thoroughly understood because of the complex genetic and environmental interactions. We identified a notched-belly (NB) mutant that has a notched-line on the belly of grains. The line dissects the endosperm into two distinct parts, the upper translucent part, and the bottom chalky part in the vicinity of the embryo. Using this mutant, our previous studies clued the negative influence of embryo on the biochemical makeup of the endosperm, suggesting the need for the in-depth study of the embryo effect on the metabolome of developing endosperm. This study continued to use the NB mutant to evolve a novel comparison method to clarify the role of embryo in the formation of a chalky endosperm. Grain samples of the wild-type (WT) and NB were harvested at 10, 20, and 30 days after fertilization (DAF), and then divided into subsamples of the embryo, the upper endosperm, and the bottom endosperm. Using non-targeted metabolomics and whole-genome RNA sequencing (RNA-seq), a nearly complete catalog of expressed metabolites and genes was generated. Results showed that the embryo impaired the storage of sucrose, amino acid, starch, and storage proteins in the bottom endosperm of NB by enhancing the expression of sugar, amino acids, and peptide transporters, and declining the expression of starch, prolamin, and glutelin synthesis-related genes. Importantly, the competitive advantage of the developing embryo in extracting the nutrients from the endosperm, transformed the bottom endosperm into an “exhaustive source” by diverting the carbon (C) and nitrogen (N) metabolism from synthetic storage to secondary pathways, resulting in impaired filling of the bottom endosperm and subsequently the formation of chalky tissue. In summary, this study reveals that embryo-induced metabolic shift in the endosperm is associated with the occurrence of grain chalkiness, which is of relevance to the development of high-quality rice by balancing the embryo–endosperm interaction.

Inline 3D Volumetric Measurement of Moisture Content in Rice Using Regression-Based ML of RF Tomographic Imaging

The moisture content of stored rice is dependent on the surrounding and environmental factors which in turn affect the quality and economic value of the grains. Therefore, the moisture content of grains needs to be measured frequently to ensure that optimum conditions that preserve their quality are maintained. The current state of the art for moisture measurement of rice in a silo is based on grab sampling or relies on single rod sensors placed randomly into the grain. The sensors that are currently used are very localized and are, therefore, unable to provide continuous measurement of the moisture distribution in the silo. To the authors’ knowledge, there is no commercially available 3D volumetric measurement system for rice moisture content in a silo. Hence, this paper presents results of work carried out using low-cost wireless devices that can be placed around the silo to measure changes in the moisture content of rice. This paper proposes a novel technique based on radio frequency tomographic imaging using low-cost wireless devices and regression-based machine learning to provide contactless non-destructive 3D volumetric moisture content distribution in stored rice grain. This proposed technique can detect multiple levels of localized moisture distributions in the silo with accuracies greater than or equal to 83.7%, depending on the size and shape of the sample under test. Unlike other approaches proposed in open literature or employed in the sector, the proposed system can be deployed to provide continuous monitoring of the moisture distribution in silos.

Novel Mutant Alleles Reveal a Role of the Extra-Large G Protein in Rice Grain Filling, Panicle Architecture, Plant Growth, and Disease Resistance

Plant growth and grain filling are the key agronomical traits for grain weight and yield of rice. The continuous improvement in rice yield is required for a future sustainable global economy and food security. The heterotrimeric G protein complex containing a canonical α subunit (RGA1) couples extracellular signals perceived by receptors to modulate cell function including plant development and grain weight. We hypothesized that, besides RGA1, three atypical, extra-large GTP-binding protein (XLG) subunits also regulate panicle architecture, plant growth, development, grain weight, and disease resistance. Here, we identified a role of XLGs in agronomic traits and stress tolerance by genetically ablating all three rice XLGs individually and in combination using the CRISPR/Cas9 genome editing in rice. For this study, eight (three single, two double, and three triple) null mutants were selected. Three XLG proteins combinatorically regulate seed filling, because loss confers a decrease in grain weight from 14% with loss of one XLG and loss of three to 32% decrease in grain weight. Null mutations in XLG2 and XLG4 increase grain size. The mutants showed significantly reduced panicle length and number per plant including lesser number of grains per panicle compared to the controls. Loss-of-function of all individual XLGs contributed to 9% more aerial biomass compared to wild type (WT). The double mutant showed improved salinity tolerance. Moreover, loss of the XLG gene family confers hypersensitivity to pathogens. Our findings suggest that the non-canonical XLGs play important roles in regulating rice plant growth, grain filling, panicle phenotype, stress tolerance, and disease resistance. Genetic manipulation of XLGs has the potential to improve agronomic properties in rice.

The Vacuolar Transporter OsNRAMP2 Mediates Fe Remobilization During Germination and Affects Cd Distribution to Rice Grain

Background and aims Iron (Fe) deficiency in plants is a common problem affecting agricultural production. Cadmium (Cd) is a toxic metal that can be taken up and transported within plants by transporters for divalent metals including Fe(II). The present study aims to investigate the functions of OsNRAMP2 (Natural Resistance-Associated Macrophage Protein 2) in the remobilization and distribution of Fe and Cd in rice. Methods The expression pattern of OsNRAMP2 was determined by quantitative real-time PCR and pOsNRAMP2:GUS assay. Knockout mutants of OsNRAMP2 were generated by using CRISPR/Cas9 gene editing. Localization of Fe in the vacuolar globoids of germinating seeds was imaged by high-resolution transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. Distributions of Fe and Cd between different plant tissues were investigated in hydroponic and soil pot experiments. Results OsNRAMP2 was mainly expressed in the embryo of germinating seeds, roots, leaf sheaths and leaf blades. OsNRAMP2 was localized at the tonoplast. Knockout of OsNRAMP2 delayed seed germination and produced chlorotic seedling leaves. Remobilization of Fe stored in the protein storage vacuoles in the scutellum of germinating seeds was restricted in osnramp2 mutants compared with wild type. Expression of genes related to Fe uptake was enhanced in the seedlings of osnramp2 mutants. Knockout of OsNRAMP2 significantly decreased the distribution of Cd, but not Fe, from leaves and straws to rice grains. Conclusions OsNRAMP2 plays an important role in remobilizing vacuolar Fe during seed germination and affects translocation of Cd from vegetative tissues to rice grains.