Genetic mapping identifies a rice naringenin O-glucosyltransferase that influences insect resistance.

Naringenin, the biochemical precursor for predominant flavonoids in grasses, provides protection against UV damage, pathogen infection and insect feeding. To identify previously unknown loci influencing naringenin accumulation in rice (Oryza sativa), recombinant inbred lines derived from the Nipponbare and IR64 cultivars were used to map a quantitative trait locus (QTL) for naringenin abundance to a region of 50 genes on rice chromosome 7. Examination of candidate genes in the QTL confidence interval identified four predicted uridine diphosphate-dependent glucosyltransferases (Os07g31960, Os07g32010, Os07g32020 and Os07g32060). In vitro assays demonstrated that one of these genes, Os07g32020 (UGT707A3), encodes a glucosyltransferase that converts naringenin and uridine diphosphate-glucose to naringenin-7-O-ß-d-glucoside. The function of Os07g32020 was verified with CRISPR/Cas9 mutant lines, which accumulated more naringenin and less naringenin-7-O-ß-d-glucoside and apigenin-7-O-ß-d-glucoside than wild-type Nipponbare. Expression of Os12g13800, which encodes a naringenin 7-O-methyltransferase that produces sakuranetin, was elevated in the mutant lines after treatment with methyl jasmonate and insect pests, Spodoptera litura (cotton leafworm), Oxya hyla intricata (rice grasshopper) and Nilaparvata lugens (brown planthopper), leading to a higher accumulation of sakuranetin. Feeding damage from O. hyla intricata and N. lugens was reduced on the Os07g32020 mutant lines relative to Nipponbare. Modification of the Os07g32020 gene could be used to increase the production of naringenin and sakuranetin rice flavonoids in a more targeted manner. These findings may open up new opportunities for selective breeding of this important rice metabolic trait.

Metabolomics and Transcriptomics Reveal that Diarylheptanoids Vary in Amomum tsao-ko Fruit Development.

Amomum tsao-ko is an important spice and medicinal plant that has received extensive attention in recent years for its high content of bioactive constituents with the potential for food additives and drug development. Diarylheptanoids are major and characteristic compounds in A. tsao-ko; however, the biochemical and molecular foundation of diarylheptanoids in fruit is unknown. We performed comparative metabolomics and transcriptomics studies in the ripening stages of A. tsao-ko fruit. The chemical constituents of fruit vary in different harvest periods, and the diarylheptanoids have a trend to decrease or increase with fruit development. GO enrichment analysis revealed that plant hormone signaling pathways including the ethylene-activated signaling pathway, salicylic acid, jasmonic acid, abscisic acid, and response to hydrogen peroxide were associated with fruit ripening. The biosynthetic pathways including phenylpropanoid, flavonoids, and diarylheptanoids biosynthesis were displayed in high enrichment levels in ripening fruit. The molecular networking and phytochemistry investigation of A. tsao-ko fruit has isolated and identified 10 diarylheptanoids including three new compounds. The candidate genes related to diarylheptanoids were obtained by coexpression network analysis and phylogenetic analysis. Two key genes have been verified to biosynthesize linear diarylheptanoids. This integrative approach provides gene regulation and networking associated with the biosynthesis of characteristic diarylheptanoids, which can be used to improve the quality of A. tsao-ko as food and medicine.

Polyamine pathways interconnect with GABA metabolic processes to mediate the low-temperature response in plants.

Low temperatures are among the most commonly encountered environmental conditions that adversely affect plant growth and development, leading to substantial reductions in crop productivity. Plants have accordingly evolved coordinated mechanisms that confer low-temperature adaptation and resistance. The plant metabolic network, including polyamines (PAs) and γ-aminobutyric acid (GABA) is reprogrammed to ensure that essential metabolic homeostasis is maintained in response to cold stress conditions. Additionally, GABA might serve as a central molecule in the defense system during low-temperature tolerance in plants. However, our understanding of how these metabolites function in conferring cold tolerance is still far from complete. Here, we summarized how PAs and GABA function in conferring cold tolerance, and describe the crucial role of GABA in the mitigation of ROS during cold stress in plants.

Chromosome-level genome assembly of Amomum tsao-ko provides insights into the biosynthesis of flavor compounds.

Amomum tsao-ko is an economically important spice plant in the ginger family (Zingiberaceae). The dried ripe fruit has been widely used as spice and medicine in Southeast Asia due to its distinct flavor metabolites. However, there is little genomic information available to understand the biosynthesis of its characteristic flavor compounds. Here, we present a high-quality chromosome-level genome of A. tsao-ko with a total length of 2.08 Gb assembled into 24 chromosomes. Potential relationships between genetic variation and chemical constituents were analyzed by a genome-wide association study of 119 representative A. tsao-ko specimens in China. Metabolome and transcriptome correlation analysis of different plant organs and fruit developmental stages revealed the proposed biosynthesis of the characteristic bicyclononane aldehydes and aromatic metabolites in A. tsao-ko fruit. Transcription factors of 20 families may be involved in the regulatory network of terpenoids. This study provides genomic and chemical insights into the biosynthesis of characteristic aroma and flavor constituents, which can be used to improve the quality of A. tsao-ko as food and medicine.

Two Splicing Variants of OsNPF7.7 Regulate Shoot Branching and Nitrogen Utilization Efficiency in Rice.

Rice includes 93 nitrate and peptide transporters family (NPF) members that facilitate the soil uptake and internal reallocation of nitrogen for growth and development. This study demonstrated that OsNPF7.7 had two splicing variants, and altered expression of each variant could regulate shoot branching and nitrogen utilization efficiency (NUtE) in rice. The expression of both variants was down-regulated in the buds by increased nitrogen level in the Japonica rice variety ZH11. The expression level of long-variant OsNPF7.7-1 was higher in panicles at reproductive stage, however, the expression level of short-variant OsNPF7.7-2 was higher in buds and leaves at vegetative stage compared to each other in ZH11. OsNPF7.7-1 was localized in the plasma membrane, whereas OsNPF7.7-2 was localized in the vacuole membrane. Furthermore, the results indicated that the expression level of each variant for OsNPF7.7 determined axillary bud outgrowth, and then influenced the rice tiller number. Overexpression of OsNPF7.7-1 could promote nitrate influx and concentration in root, whereas overexpression of OsNPF7.7-2 could improve ammonium influx and concentration in root. RNAi and osnpf7.7 lines of OsNPF7.7 showed an increased amount of amino acids in leaf sheaths, but a decreased amount in leaf blades, which affected nitrogen allocation and plant growth. The elevated expression of each variant for OsNPF7.7 in ZH11 enhanced NUtE using certain fertilization regimes under paddy field conditions. Moreover, overexpression of each variant for OsNPF7.7 in KY131 increased significantly the filled grain number per plant. Thus, increased each variant of OsNPF7.7 has the potential to improve grain yield and NUtE in rice.

The Rice Peptide Transporter OsNPF7.3 Is Induced by Organic Nitrogen, and Contributes to Nitrogen Allocation and Grain Yield.

Nitrogen use efficiency is important for the development of sustainable agriculture. Plants have different transporters to facilitate nitrogen uptake and internal distribution. This study demonstrates that the peptide transporter OsNPF7.3 enhances nitrogen allocation and increases grain yield in rice. OsNPF7.3 is a member of the nitrate transporter 1/peptide transporter family (NPF) and is localized in the vacuolar membrane. Its expression is higher in the lateral roots and stems. Its transcripts concentrate in the vascular bundle and significantly regulated by organic nitrogen sources. The RNAi lines of OsNPF7.3 affect plant growth and cause amino acids to accumulate in leaf sheaths and decrease in the leaf blades. At later stages of reproductive growth, nitrogen degradation accelerates in the leaves of plants over-expressing OsNPF7.3 and the nitrogen is translocated to grains. The tiller numbers, panicles per plant, filled grain numbers per panicle, and grain nitrogen content of the OsNPF7.3 over-expressing plant were more than that of wide type. The elevated gene expression in OsNPF7.3 could enhance nitrogen utilization efficiency in rice paddy.