Analysis of malto-oligosaccharides and related metabolites in rice endosperm during development

Transcriptome and Metabolome Analyses Reveals the Pathway and Metabolites of Grain Quality Under Phytochrome B in Rice (Oryza sativa L.)

BACKGROUND

Grain size and chalkiness is a critical agronomic trait affecting rice yield and quality. The application of transcriptomics to rice has widened the understanding of complex molecular responsive mechanisms, differential gene expression, and regulatory pathways under varying conditions. Similarly, metabolomics has also contributed drastically for rice trait improvements. As master regulators of plant growth and development, phys influence seed germination, vegetative growth, photoperiodic flowering, shade avoidance responses. OsPHYB can regulate a variety of plant growth and development processes, but little is known about the roles of rice gene OsPHYB in modulating grain development.

RESULTS

In this study, rice phytochrome B (OsPHYB) was edited using CRISPR/Cas9 technology. We found that OsPHYB knockout increased rice grain size and chalkiness, and increased the contents of amylose, free fatty acids and soluble sugar, while the gel consistency and contents of proteins were reduced in mutant grains. Furthermore, OsPHYB is involved in the regulation of grain size and chalk formation by controlling cell division and complex starch grain morphology. Transcriptomic analysis revealed that loss of OsPHYB function affects multiple metabolic pathways, especially enhancement of glycolysis, fatty acid, oxidative phosphorylation, and antioxidant pathways, as well as differential expression of starch and phytohormone pathways. An analysis of grain metabolites showed an increase in the free fatty acids and lysophosphatidylcholine, whereas the amounts of sugars, alcohols, amino acids and derivatives, organic acids, phenolic acids, alkaloids, nucleotides and derivatives, and flavonoids decreased, which were significantly associated with grain size and chalk formation.

CONCLUSIONS

Our study reveals that, OsPHYB plays an important regulatory role in the growth and development of rice grains, especially grain size and chalkiness. Furthermore, OsPHYB regulates grain size and chalkiness formation by affecting gene metabolism interaction network. Thus, this study not only revealed that OsPHYB plays a vital role in regulating grain size and chalkiness of rice but reveal new functions and highlighted the importance and value of OsPHYB in rice grain development and provide a new strategy for yield and quality improvement in rice breeding.

Malto-oligosaccharides as critical functional ingredient: a review of their properties, preparation, and versatile applications

Malto-oligosaccharides (MOS) are α-1,4 glycosidic linked linear oligosaccharides of glucose, which have a diverse range of functional applications in the food, pharmaceutical, and other industries. They can be used to modify the physicochemical properties of foods thereby improving their quality attributes, or they can be included as prebiotics to improve their nutritional attributes. The degree of polymerization of MOS can be controlled by using specific enzymes, which means their functionality can be tuned for specific applications. In this article, we review the chemical structure, physicochemical properties, preparation, and functional applications of MOS in the food, health care, and other industries. Besides, we offer an overview for this saccharide from the perspective of prospect functional ingredient, which we feel lacks in the current literature. MOS could be expected to provide a novel promising substitute for functional oligosaccharides.

Changes in fine structure of amylopectin and internal structures of starch granules in developing endosperms and culms caused by starch branching enzyme mutations of japonica rice

BEIIb plays a specific role in determining the structure of amylopectin in rice endosperm, whereas BEIIa plays the similar role in the culm where BEIIb is absent. Cereals have three types of starch branching enzymes (BEs), BEI, BEIIa, and BEIIb. It is widely known that BEIIb is specifically expressed in the endosperm and plays a distinct role in the structure of amylopectin because in its absence the amylopectin type changes to the amylose-extender-type (ae-type) or B-type from the wild-type or A-type and this causes the starch crystalline allomorph to the B-type from the wild-type A-type. This study aimed to clarify the role of BEIIa in the culm where BEIIb is not expressed, by using a be2a mutant in comparison with results with be2b and be1 mutants. The results showed that the amylopectin structure exhibited the B-type in the be2a culm compared with the A-type in the wild-type culm. The starch granules from the be2a culm also showed the B-type like allomorph when examined by X-ray diffraction analysis and optical sum frequency generation spectroscopy. Both amylopectin chain-length profile and starch crystalline properties were found to be the A-type at the very early stage of endosperm development at 4-6 days after pollination (DAP) even in the be2b mutant. All these results support a view that in the culm as well as in the endosperm at 4-6 DAP, BEIIa can play the role of BEIIb which has been well documented in maturing endosperm. The possible mechanism as to how BEIIa can play its role is discussed.