Producing fast and active Rubisco in tobacco to enhance photosynthesis.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) performs most of the carbon fixation on Earth. However, plant Rubisco is an intrinsically inefficient enzyme given its low carboxylation rate, representing a major limitation to photosynthesis. Replacing endogenous plant Rubisco with a faster Rubisco is anticipated to enhance crop photosynthesis and productivity. However, the requirement of chaperones for Rubisco expression and assembly has obstructed the efficient production of functional foreign Rubisco in chloroplasts. Here, we report the engineering of a Form 1A Rubisco from the proteobacterium Halothiobacillus neapolitanus in Escherichia coli and tobacco (Nicotiana tabacum) chloroplasts without any cognate chaperones. The native tobacco gene encoding Rubisco large subunit was genetically replaced with H. neapolitanus Rubisco (HnRubisco) large and small subunit genes. We show that HnRubisco subunits can form functional L8S8 hexadecamers in tobacco chloroplasts at high efficiency, accounting for ∼40% of the wild-type tobacco Rubisco content. The chloroplast-expressed HnRubisco displayed a ∼2-fold greater carboxylation rate and supported a similar autotrophic growth rate of transgenic plants to that of wild-type in air supplemented with 1% CO2. This study represents a step toward the engineering of a fast and highly active Rubisco in chloroplasts to improve crop photosynthesis and growth.

The elite eating quality alleles Wxb and ALKb are regulated by OsDOF18 and coordinately improve head rice yield.

Head rice yield (HRY) measures rice milling quality and determines final grain yield and commercial value. Here, we report that two major quantitative trait loci for milling quality in rice, qMq-1 and qMq-2, represent allelic variants of Waxylv/Waxyb (hereafter Wx) encoding Granule-Bound Starch Synthase I (GBSSI) and Alkali Spreading Value ALKc/ALKb encoding Soluble Starch Synthase IIa (SSIIa), respectively. Complementation and overexpression transgenic lines in indica and japonica backgrounds confirmed that Wx and ALK coordinately regulate HRY by affecting amylose content, the number of amylopectin branches, amyloplast size, and thus grain filling and hardness. The transcription factor OsDOF18 acts upstream of Wx and ALK by activating their transcription. Furthermore, rice accessions with Wxb and ALKb alleles showed improved HRY over those with Wxlv and ALKc. Our study not only reveals the novel molecular mechanism underlying the formation of HRY but also provides a strategy for breeding rice cultivars with improved HRY.

SvSTL1 in the large subunit family of ribonucleotide reductases plays a major role in chloroplast development of Setaria viridis.

Ribonucleotide reductases (RNRs) are essential enzymes in DNA synthesis. However, little is known about the RNRs in plants. Here, we identified a svstl1 mutant from the self-created ethyl methanesulfonate (EMS) mutant library of Setaria viridis. The mutant leaves exhibited a bleaching phenotype at the heading stage. Paraffin section analysis showed the destruction of the C4 Kranz anatomy. Transmission electron microscopy results further demonstrated the severely disturbed development of some chloroplasts. MutMap analysis revealed that the SvSTL1 gene is the primary candidate, encoding a large subunit of RNRs. Complementation experiments confirmed that SvSTL1 is responsible for the phenotype of svstl1. There are two additional RNR large subunit homologs in S. viridis, SvSTL2 and SvSTL3. To further understand the functions of these three RNR large subunit genes, a series of mutants were generated via CRISPR/Cas9 technology. In striking contrast to the finding that all three SvSTLs interact with the RNR small subunit, the phenotype varied along with the copies of chloroplast genome among different svstl single mutants: the svstl1 mutant exhibited pronounced chloroplast development and significantly fewer copies of the chloroplast genome than the svstl2 or svstl3 single mutants. These results suggested that SvSTL1 plays a major role in the optimal function of RNRs and is essential for chloroplast development. Furthermore, through the analysis of double and triple mutants, the study provides new insights into the finely tuned coordination among SvSTLs to maintain normal chloroplast development in the emerging C4 model plant S. viridis.

The microRNA-7322-5p/p38/Hsp19 axis modulates Chilo suppressalis cell-defences against Cry1Ca: an effective target for a stacked transgenic rice approach.

Bacillus thuringiensis (Bt)-secreted crystal (Cry) toxins form oligomeric pores in host cell membranes and are a common element in generating insect-resistant transgenic crops. Although Cry toxin function has been well documented, cellular defences against pore-formation have not been as well developed. Elucidation of the processes underlying this defence, however, could contribute to the development of enhanced Bt crops. Here, we demonstrate that Cry1Ca-mediated downregulation of microRNA-7322-5p (miR-7322-5p), which binds to the 3' untranslated region of p38, negatively regulates the susceptibility of Chilo suppressalis to Cry1Ca. Moreover, Cry1Ca exposure enhanced phosphorylation of Hsp19, and hsp19 downregulation increased susceptibility to Cry1Ca. Further, Hsp19 phosphorylation occurs downstream of p38, and pull-down assays confirmed the interactions between Hsp19 and Cry1Ca, suggesting that activation of Hsp19 by the miR-7322-5p/p38/Hsp19 pathway promotes Cry1Ca sequestration. To assess the efficacy of targeting this pathway in planta, double-stranded RNA (dsRNA) targeting C. suppressalis p38 (dsp38) was introduced into a previously generated cry1Ca-expressing rice line (1CH1-2) to yield a single-copy cry1Ca/dsp38 rice line (p38-rice). Feeding on this rice line triggered a significant reduction in C. suppressalis p38 expression and the line was more resistant to C. suppressalis than 1CH1-2 in both short term (7-day) and continuous feeding bioassays as well as field trials. These findings provide new insights into invertebrate epithelium cellular defences and demonstrate a potential new pyramiding strategy for Bt crops.

Knockdown of Dcr1 and Dcr2 limits the lethal effect of C-factor in Chilo suppressalis.

Dicer is a highly conserved ribonuclease in evolution. It belongs to the RNase III family and can specifically recognize and cleave double-stranded RNA (dsRNA). In this study, the genome and transcriptome of Chilo suppressalis were analyzed, and it was found that there were two members in the Dicer family, named Dcr1 and Dcr2. The dsRNAs of Dcr1 and Dcr2 genes were synthesized and fed to C. suppressalis larvae. The C-factor of C. suppressalis was selected as the marker gene. The results showed that both Dcr1 and Dcr2 genes were significantly knocked down. The larval mortality was significantly reduced by 43.50% (p < 0.05) after feeding on dsC-factor and dsDcr1. The transcription levels of C-factor genes were significantly increased by 33.95% (p < 0.05) and 32.94% (p < 0.05) when the larvae fed with dsDcr2 + dsC-factor for 72 h and 96 h, respectively. Furthermore, the mortality was significantly decreased by 79% (p < 0.05) after feeding dsC-factor and dsDcr2. These findings imply that Dcr1 can decrease the lethal effect of C-factor gene but cannot affect its RNAi efficiency and Dcr2 can decrease the lethal effect of C-factor gene by inhibiting RNAi efficiency.

Expression and clinical significance of NRLP1 in patients with ST-segment elevation myocardial infarction combined with malignant ventricular arrhythmia.

Objective: To investigate the clinical effects of NRLP1 expression in patients with ST-segment elevation myocardial infarction (STEMI) combined with arrhythmia. Methods: We enrolled 231 patients with STEMI in the first hospital of Quanzhou affiliated to Fujian Medical University from January 2019 to December 2020 to the observational group and 230 healthy individuals as the control group. We divided patients with STEMI into a malignant ventricular arrhythmia (MVA) group (n=36) and non-MVA(NMVA) group (n=195) depending on whether the individuals had experienced an episode of MVA within 48 hours after PCI. We recorded general variables such as age, gender, history of smoking, hypertension, of diabetes, hyperlipidemia, left ventricular ejection fraction (LVEF), Gensini score, and mortality. Moreover, we determined NLRP1, IL-1ß, TNF-α, high-sensitivity C-reactive protein (hs-CRP), N-terminal pro-brain natriuretic peptide (NT-pro-BNP), cardiac troponin-1 (cTnI), and creatine kinase isoenzyme (CK-MB) in peripheral blood by ELISA. Results: We found significant differences in LVEF, Gensini scores, smoking history, and mortality between the MVA and NMVA groups. The mean NLRP1 expression was highest in the MVA group, which was positively correlated with the levels of IL-1ß, TNF-α, hs-CRP, NT-pro-BNP, cTnI and CK-MB. The expression of NLRP1 was associated with the smoking history, the LVEF value, the Gensini score, the MVA incidence and the mortality. Patients with higher NLRP1 expression levels had a higher MACE incidence and worse overall survivals within one year. Conclusion: The NLRP1 pathway is associated with the presence of arrhythmias after PCI treatments, and the NLRP1 expression level may be useful as a predictor of arrhythmia in patients with STEMI.

Isolation and functional analysis of OsAOS1 promoter for resistance to Nilaparvata lugens Stål infestation in rice.

Insect pests have a great impact on the yield and quality of crops. Insecticide applications are an effective method of pest control, however, they also have adverse effects on the environment. Using insect-inducible promoters to drive insect-resistant genes in transgenic crops is a potential sustainable pest management strategy, but insect-inducible promoters have been rarely reported. In this study, we found rice allene oxide synthase gene (AOS, LOC_Os03g12500) can be highly upregulated following brown planthopper (Nilaparvata lugens Stål, BPH) infestation. Then, we amplified the promoter of OsAOS1 and the ß- glucuronidase reporter gene was used to analyze the expression pattern of the promoter. Through a series of 5' truncated assays, three positive regulatory regions in response to BPH infestation in the promoter were identified. The transgenic plants, P1R123-min 35S and P1TR1-min 35S promoter-driven snowdrop lectin (Galanthus nivalis agglutinin, GNA) gene, demonstrated the highest expression levels of GNA and lowest BPH survival. Our work identified a BPH-inducible promoter and three positive regions within it. Transgenic rice with GNA driven by OsAOS1 promoter and positive regions exhibited an expected lethal effect on BPH. This study proved the application potential of BPH-inducible promoter and provided a novel path for the selection of insect-resistant tools in the future.

Nanoparticle facilitated stacked-dsRNA improves suppression of the Lepidoperan pest Chilo suppresallis.

BACKGROUND: In recent years, gene knockdown technology using double-stranded RNA (dsRNA) has been widely used as an environment-friendly pest control strategy, but its instability and limited cellular uptake have limited its overall effect. Studies have shown that the efficiency of single dsRNA can be improved by using various nanomaterials. However, the effect of stacked-dsRNA wrapped by nanomaterial on pests remains unclear. In the present study, both CYP15C1 and C-factor genes were cloned from the midgut of C. suppressalis, and the transcript of C-factor is most highly expressed in heads. Feeding a dsCYP15C1 or dsC-factor - nanomaterial mixture can downregulate the gene expression and significantly increase larval mortality. More importantly, feeding the stacked-dsRNA wrapped by nanomaterial can significantly increase the mortality of C. suppressalis, compared with feeding dsCYP15C1 or dsC-factor - nanomaterial mixture alone. These results showed that CYP15C1 and C-factor could be potential targets for an effective management of C. suppressalis, and we developed a nanoparticle-facilitated stacked-dsRNA strategy in the control of C. suppresallis. Our research provides a theoretical basis for gene function analysis and field pest control, and will promote the application of RNAi technology in the stacked style of pest control.

Improvement of Rice Agronomic Traits by Editing Type-B Response Regulators.

Type-B response regulator proteins in rice contain a conserved receiver domain, followed by a GARP DNA binding domain and a longer C-terminus. Some type-B response regulators such as RR21, RR22 and RR23 are involved in the development of rice leaf, root, flower and trichome. In this study, to evaluate the application potential of type-B response regulators in rice genetic improvement, thirteen type-B response regulator genes in rice were respectively knocked out by using CRISPR/Cas9 genome editing technology. Two guide RNAs (gRNAs) were simultaneously expressed on a knockout vector to mutate one gene. T0 transformed plants were used to screen the plants with deletion of large DNA fragments through PCR with specific primers. The mutants of CRISPR/Cas9 gene editing were detected by Cas9 specific primer in the T1 generation, and homozygous mutants without Cas9 were screened, whose target regions were confirmed by sequencing. Mutant materials of 12 OsRRs were obtained, except for RR24. Preliminary phenotypic observation revealed variations of various important traits in different mutant materials, including plant height, tiller number, tillering angle, heading date, panicle length and yield. The osrr30 mutant in the T2 generation was then further examined. As a result, the heading date of the osrr30 mutant was delayed by about 18 d, while the yield was increased by about 30%, and the chalkiness was significantly reduced compared with those of the wild-type under field high temperature stress. These results indicated that osrr30 has great application value in rice breeding. Our findings suggest that it is feasible to perform genetic improvement of rice by editing the type-B response regulators.

Repressed OsMESL expression triggers reactive oxygen species-mediated broad-spectrum disease resistance in rice.

A few reports have indicated that a single gene confers resistance to bacterial blight, sheath blight and rice blast. In this study, we identified a novel disease resistance mutant gene, methyl esterase-like (osmesl) in rice. Mutant rice with T-DNA insertion displayed significant resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo), sheath blight caused by Rhizoctonia solani and rice blast caused by Magnaporthe oryzae. Additionally, CRISPR-Cas9 knockout mutants and RNAi lines displayed resistance to these pathogens. Complementary T-DNA mutants demonstrated a phenotype similar to the wild type (WT), thereby indicating that osmesl confers resistance to pathogens. Protein interaction experiments revealed that OsMESL affects reactive oxygen species (ROS) accumulation by interacting with thioredoxin OsTrxm in rice. Moreover, qRT-PCR results showed significantly reduced mRNA levels of multiple ROS scavenging-related genes in osmesl mutants. Nitroblue tetrazolium staining showed that the pathogens cause ROS accumulation, and quantitative detection revealed significantly increased levels of H2 O2 in the leaves of osmesl mutants and RNAi lines after infection. The abundance of JA, a hormone associated with disease resistance, was significantly more in osmesl mutants than in WT plants. Overall, these results suggested that osmesl enhances disease resistance to Xoo, R. solani and M. oryzae by modulating the ROS balance.

The PPR-SMR Protein ATP4 Is Required for Editing the Chloroplast rps8 mRNA in Rice and Maize.

Chloroplast gene expression involves the participation of hundreds of pentatricopeptide repeat (PPR) RNA binding proteins, and proteins in the PLS subfamily typically specify sites of RNA editing, whereas those in the P-subfamily typically stabilize RNA, activate translation, or promote intron splicing. Several P-type PPR proteins include a small MutS-related (SMR) domain, but the biochemical contribution of the SMR domain remains enigmatic. Here, we describe a rice (Oryza sativa) mutant, osatp4, lacking the ortholog of ATP4, a PPR-SMR protein in maize (Zea mays). osatp4 mutants were chlorotic and had a plastid-ribosome deficiency when grown in the cold. Like maize ATP4, OsATP4 was required for the accumulation of dicistronic rpl16-rpl14 transcripts. Surprisingly, OsATP4 was also required for the editing of a specific nucleotide in the ribosomal protein S8 transcripts, rps8, and this function was conserved in maize. By contrast, rps8 RNA was edited normally in the maize PROTON gradient regulation3 mutant, pgr3, which also lacks rpl16-rpl14 transcripts, indicating that the editing defect in atp4 mutants is not a secondary effect of altered rpl16-rpl14 RNA metabolism. Expression of the edited rps8 isoform in transgenic osatp4 mutants complemented the cold-sensitive phenotype, indicating that a rps8 expression defect accounts for the cold-sensitivity. We suggest that ATP4 stimulates rps8 editing by facilitating access of a previously characterized PLS-type RNA editing factor to its cognate cis-element upstream of the edited nucleotide.

Overexpression of the homoterpene synthase gene, OsCYP92C21, increases emissions of volatiles mediating tritrophic interactions in rice.

Plant defence homoterpenes can be used to attract pest natural enemies. However, the biosynthetic pathway of homoterpenes is still unknown in rice, and the practical application of such indirect defence systems suffers from inherent limitations due to their low emissions from plants. Here, we demonstrated that the protein OsCYP92C21 is responsible for homoterpene biosynthesis in rice. We also revealed that the ability of rice to produce homoterpenes is dependent on the subcellular precursor pools. By increasing the precursor pools through specifically subcellular targeting expression, genetic transformation and genetic introgression, we significantly enhanced homoterpene biosynthesis in rice. The final introgressed GM rice plants exhibited higher homoterpene emissions than the wild type rice and the highest homoterpene emission reported so far for such GM plants even without the induction of herbivore attack. As a result, these GM rice plants demonstrated strong attractiveness to the parasitic wasp Cotesia chilonis. This study discovered the homoterpene biosynthesis pathway in rice, and lays the foundation for the utilisation of plant indirect defence mechanism in the "push-pull" strategy of integrated pest management through increasing precursor pools in the subcellular compartments and overexpressing homoterpene synthase by genetic transformation.

Salt-induced inhibition of rice seminal root growth is mediated by ethylene-jasmonate interaction.

The phytohormones ethylene and jasmonate play important roles in the adaptation of rice plants to salt stress. However, the molecular interactions between ethylene and jasmonate on rice seminal root growth under salt stress are unknown. In this study, the effects of NaCl on the homeostasis of ethylene and jasmonate, and on rice seminal root growth were investigated. Our results indicate that NaCl treatment promotes ethylene biosynthesis by up-regulating the expression of ethylene biosynthesis genes, whereas NaCl-induced ethylene does not inhibit rice seminal root growth directly, but rather indirectly, by promoting jasmonate biosynthesis. NaCl treatment also promotes jasmonate biosynthesis through an ethylene-independent pathway. Moreover, NaCl-induced jasmonate reduces meristem cell number and cell division activity via down-regulated expression of Oryza sativa PLETHORA (OsPLT) and cell division-related genes, respectively. Additionally, NaCl-induced jasmonate inhibits seminal root cell elongation by down-regulating the expression of cell elongation-related genes. Overall, salt stress promotes jasmonate biosynthesis through ethylene-dependent and -independent pathways in rice seminal roots, and jasmonate inhibits rice seminal root growth by inhibiting root meristem cell proliferation and root cell elongation.

OsMYB3 is a R2R3-MYB gene responsible for anthocyanin biosynthesis in black rice.

Black rice is a rare type of rice germplasm with various health benefits that are largely attributed to anthocyanin pigment accumulation in the pericarps. The anthocyanin biosynthesis in plant tissues is activated mainly by the MBW complexes, consisting of three types of transcription factors R2R3-MYB, bHLH, and WDR. In black rice, the bHLH and WDR components regulating anthocyanin biosynthesis in pericarps have been characterized, while the R2R3-MYB factor remains unknown. By examining the expression correlation between all putative rice MYB genes and anthocyanin biosynthesis-related genes based on transcriptome data of pericarps in combination with further molecular and genetic analysis, we proved that OsMYB3 (LOC_Os03g29614) was the determinant R2R3-MYB gene for anthocyanin biosynthesis in rice pericarps. The expression level of OsMYB3 in pericarps of black rice was significantly higher than that of white rice. The knockout of OsMYB3 in a black rice variety caused significant downregulation of 19 anthocyanin metabolites and many other flavonoids in grains. Our research deepens the understanding of regulatory system for anthocyanin biosynthesis in rice pericarps and provides implications for breeding black rice varieties with high anthocyanin level. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-021-01244-x.

Cloning and RNAi-mediated three lethal genes that can be potentially used for Chilo suppressalis (Lepidoptera: Crambidae) management.

RNA interference (RNAi) has gained attention in recent years as a viable pest control strategy. Here, RNAi assays were performed to screen the potential functionality of genes in Chilo suppressalis, a serious pest of rice, and to determine their potential for developing a highly targeted molecular control approach. Potential homologs of NADH dehydrogenase (ND), glycerol 3-phosphate dehydrogenase (GPDH) and male specific lethal 3 (MSL3) were cloned from C. suppressalis, and their spatiotemporal gene expression evaluated. The expression of all three genes was higher in the pupal and adult stages than the larval stages and largely higher in the larval head compared to other tissues. Newly hatched larvae exhibited high mortalities and suppressed growth when fed bacteria producing double-stranded RNAs (dsRNAs) corresponding to the three target genes. This study provides insights into the function of ND, GPDH and MSL3 during C. suppressalis larval development and suggests that all may be candidate gene targets for C. suppressalis pest management.

Molecular and Genetic Aspects of Grain Number Determination in Rice (Oryza sativa L.).

Rice grain yield is a complex trait determined by three components: panicle number, grain number per panicle (GNPP) and grain weight. GNPP is the major contributor to grain yield and is crucial for its improvement. GNPP is determined by a series of physiological and biochemical steps, including inflorescence development, formation of rachis branches such as primary rachis branches and secondary rachis branches, and spikelet specialisation (lateral and terminal spikelets). The molecular genetic basis of GNPP determination is complex, and it is regulated by numerous interlinked genes. In this review, panicle development and the determination of GNPP is described briefly, and GNPP-related genes that influence its determination are categorised according to their regulatory mechanisms. We introduce genes related to rachis branch development and their regulation of GNPP, genes related to phase transition (from rachis branch meristem to spikelet meristem) and their regulation of GNPP, and genes related to spikelet specialisation and their regulation of GNPP. In addition, we describe other GNPP-related genes and their regulation of GNPP. Research on GNPP determination suggests that it is possible to cultivate rice varieties with higher grain yield by modifying GNPP-related genes.

Comprehensive construction strategy of bidirectional green tissue-specific synthetic promoters.

Bidirectional green tissue-specific promoters have important application prospects in genetic engineering and crop genetic improvement. However, there is no report on the application of them, mainly due to undiscovered natural bidirectional green tissue-specific promoters and the lack of a comprehensive approach for the synthesis of these promoters. In order to compensate for this vacancy, the present study reports a novel strategy for the expression regulatory sequence selection and the bidirectional green tissue-specific synthetic promoter construction. Based on this strategy, seven promoters were synthesized and introduced into rice by agrobacterium-mediated transformation. The functional identification of these synthetic promoters was performed by the expression pattern of GFP and GUS reporter genes in two reverse directions in transgenic rice. The results indicated that all the synthetic promoters possessed bidirectional expression activities in transgenic rice, and four synthetic promoters (BiGSSP2, BiGSSP3, BiGSSP6, BiGSSP7) showed highly bidirectional expression efficiencies specifically in green tissues (leaf, sheath, panicle, stem), which could be widely applied to agricultural biotechnology. Our study provided a feasible strategy for the construction of synthetic promoters, and we successfully created four bidirectional green tissue-specific synthetic promoters. It is the first report on bidirectional green tissue-specific promoters that could be efficiently applied in genetic engineering.

Natural variation at OsCERK1 regulates arbuscular mycorrhizal symbiosis in rice.

The symbiotic interaction between arbuscular mycorrhizal fungi (AMF) and land plants is essential for efficient nutrient acquisition and utilisation. Our understanding of key processes controlling the AMF colonisation in rice is still limited. Dongxiang wild rice (DY) exhibited a stronger colonisation with Rhizophagus irregularis than the rice cultivar Zhongzao 35 (ZZ35). Chromosome segment substitution lines were constructed and the OsCERK1 gene from DY was mapped. Transgenic plants in the japonica rice Zhonghua 11 (ZZ11) were constructed to compare root colonisation by AMF. Chromosome single-segment substitution lines containing OsCERK1DY showed higher phosphorus content and grain yield relative to ZZ35. Four amino acids substitutions were identified among the OsCERK1 haplotypes of DY, ZZ35 and ZH11 and two of these were in the second lysine-motif domain, which is essential for the differences of AMF colonisation level among rice varieties. Heterologous expression of OsCERK1DY in ZH11 significantly enhanced AMF colonisation and increased resistance against the pathogenic fungi Magnaporthe oryzae. Notably, the OsCERK1DY haplotype was absent from 4660 cultivated rice varieties. We conclude that OsCERK1 is a key gene affecting the symbiotic interaction with AMF and OsCERK1DY has the biotechnological potential to increase rice phosphorus acquisition and utilisation efficiency for sustainable agriculture.

Accumulation of the RNA polymerase subunit RpoB depends on RNA editing by OsPPR16 and affects chloroplast development during early leaf development in rice.

Plastid-encoded genes are coordinately transcribed by the nucleus-encoded RNA polymerase (NEP) and the plastid-encoded RNA polymerase (PEP). Resulting primary transcripts are frequently subject to RNA editing by cytidine-to-uridine conversions at specific sites. The physiological role of many editing events is largely unknown. Here, we have used the CRISPR/Cas9 technique in rice to knock out a member of the PLS-DYW subfamily of pentatricopeptide repeat (PPR) proteins. We found that OsPPR16 is responsible for a single editing event at position 545 in the chloroplast rpoB messenger RNA (mRNA), resulting in an amino acid change from serine to leucine in the ß-subunit of the PEP. In striking contrast to loss-of-function mutations of the putative orthologue in Arabidopsis, which were reported to have no visible phenotype, knockout of OsPPR16 leads to impaired accumulation of RpoB, reduced expression of PEP-dependent genes, and a pale phenotype during early plant development. Thus, by editing the rpoB mRNA, OsPPR16 is required for faithful plastid transcription, which in turn is required for Chl synthesis and efficient chloroplast development. Our results provide new insights into the interconnection of the finely tuned regulatory mechanisms that operate at the transcriptional and post-transcriptional levels of plastid gene expression.

Improving nutritional quality of rice for human health.

KEY MESSAGE: This review surveys rice nutritional value, mainly focusing on breeding achievements via adoption of both genetic engineering and non-transgenic strategies to improve key nutrients associated with human health. Rice (Oryza sativa) is an essential component of the diets and livelihoods of over 3.5 billion people. Polished rice is mostly consumed as staple food, fulfilling daily energy demands and part of the protein requirement. Brown rice is comparatively more nutritious, containing more lipids, minerals, vitamins, dietary fiber, micronutrients, and bioactive compounds. In this article, we review the nutritional facts about rice including the level of γ-aminobutyric acid, resistant starch, lysine, iron, zinc, ß-carotene, folate, anthocyanin, various carotenoids, and flavonoids, focusing on their synthesis and metabolism and the advances in their biofortification via adoption of both conventional and genetic engineering strategies. We conclude that besides representing a staple food, rice has the potential to become a source of various essential nutrients or bioactive compounds through appropriate genetic improvements to benefit human health and prevent certain chronic diseases. Finally, we discuss the available, non-genetically engineering strategies for the nutritional improvement of rice, including their main strengths and constraints.