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28 March 2022, Volume 29 Issue 2 Previous Issue    Next Issue
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Letter

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Screening of Rice Germplasm and Processing Methods to Produce Low Glycemic Rice Sali Atanga Ndindeng, Koichi Futakuchi, Marie-Noelle Ndjiondjop 2022, 29(2): 101-104.  DOI: 10.1016/j.rsci.2022.01.001 Abstract ( )   HTML ( )   PDF (25738KB) ( )

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Recent Insights into Signaling Responses to Cope Drought Stress in Rice Muhammad Mahran Aslam, Muhammad Abdul Rehman Rashid, Mohammad Aquil Siddiqui, Muhammad Tahir Khan, Fozia Farhat, Shafquat Yasmeen, Imtiaz Ahmad Khan, Shameem Raja, Fatima Rasool, Mahboob Ali Sial, Zhao Yan 2022, 29(2): 105-117.  DOI: 10.1016/j.rsci.2021.08.001 Abstract ( )   HTML ( )   PDF (26244KB) ( )   Drought is one of the hot topics needing urgent attention in the current era of climate change. It massively disturbs the rice growth and productivity and is becoming a serious threat. The drought avoidance strategies in rice include stomatal closure, cellular adaptation and changes in root development. Moreover, the endogenous plant hormones (abscisic acid and jasmonic acid) and reactive oxygen species have paramount importance in drought tolerance in rice. The drought tolerance induces modification in biochemical, molecular and physiological properties of plants. At the molecular level, expression of several transcription-factors is modulated which further determine the activation of drought responsive gene families. Mitogen activated protein kinases and Ca signaling pathways initiate an array of signaling cascade for mediating the gene expression in rice. Approaches, conventional breeding methods combined with modern emerging techniques such as genetic engineering, to improve rice drought tolerance were discussed. This review provided recent insights into major regulatory factors against drought stress, signaling mechanisms and molecular engineering strategies (including conventional transgenic and recent genome editing approaches) to induce drought tolerance in rice.

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Genetic Improvement of Rice for Bacterial Blight Resistance: Present Status and Future Prospects R. Abdul Fiyaz, D. Shivani, K. Chaithanya, K. Mounika, M. Chiranjeevi, G. S. Laha, B. C. Viraktamath, L. V. Subba Rao, R. M. Sundaram 2022, 29(2): 118-132.  DOI: 10.1016/j.rsci.2021.08.002 Abstract ( )   HTML ( )   PDF (25522KB) ( )   The production and productivity of rice has been challenged due to biotic and abiotic factors. Bacterial blight (BB) disease, caused by Xanthomonas oryzae pv. oryzae, is one of the important biotic stress factors, which reduces rice production by 20%-50%. The deployment of host plant resistance is the most preferred strategy for management of BB disease, and breeding disease resistant varieties remains a very economical and effective option. However, it is difficult to develop rice varieties with durable broad-spectrum resistance against BB using conventional approaches alone. Modern biotechnological tools, particularly the deployment of molecular markers, have facilitated the cloning, characterization and introgression of BB resistance genes into elite varieties. At least 46 BB resistance genes have been identified and mapped from diverse sources till date. Among these, 11 genes have been cloned and characterized. Marker-assisted breeding remains the most efficient approach to improve BB resistance by introducing two or more resistance genes into target varieties. Among the identified genes, xa5, xa13 and Xa21 are being widely used in marker-assisted breeding and more than 70 rice varieties or hybrid rice parental lines have been improved for their BB resistance alone or in combination with genes/QTLs conferring tolerance to other stress. We review the developments related to identification and utilization of various resistance genes to develop BB resistant rice varieties through marker-assisted breeding.

Research Paper

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Improving Rice Blast Resistance by Mining Broad-Spectrum Resistance Genes at Pik Locus Zhou Ying, Wan Tao, Yuan Bin, Lei Fang, Chen Meijuan, Wang Qiong, Huang Ping, Kou Shuyan, Qiu Wenxiu, Liu Li 2022, 29(2): 133-142.  DOI: 10.1016/j.rsci.2022.01.002 Abstract ( )   HTML ( )   PDF (42082KB) ( )   Magnaporthe oryzae is known for its genetic diversity and pathogenic variability, leading to rapid breakdown of resistance in rice. Incorporating multiple broad-spectrum blast resistance genes into rice cultivars would extend disease resistance longevity. Effective resistance breeding in rice therefore requires continual enrichment of the reservoir of resistance genes and alleles. We conducted a large-scale screen of rice blast resistance in about 2 000 rice accessions. Among them, 247 accessions showed at least medium resistance to the natural infection of rice blast and 7 novel Pik alleles were identified from them. Variations in gene sequences were then correlated with the phenotypic trait to enable the identification of favorable alleles. Among the seven novel Pik alleles, the resistant rate of Pik-R0/ME/7017 donors was greater than 80%, and the disease score was less than 3. Through molecular marker-assisted backcross breeding, we successfully transferred the three Pik alleles, Pik-R0/ME/7017, into an elite cultivated line Kongyu 131 to obtain BC3F2 lines, which showed enhanced resistance to rice blast compared with the recurrent parent. Assessment of these near-isogenic lines in the greenhouse using 31 isolates of M. oryzae from Heilongjiang Province of China revealed that the resistant levels of the BC3F2 lines with Pik-R0/ME/7017 were significantly higher than those of the established cloned resistance genes Pik-m and Pi1. Exploring such alleles will enrich our gene library for resistance to rice blast.

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Cloning and Functional Analysis of Calcineurin Subunits A and B in Development and Fecundity of Nilaparvata lugens (Stål) Wang Weixia, Zhu Tingheng, Wan Pinjun, Wei Qi, He Jiachun, Lai Fengxiang, Fu Qiang 2022, 29(2): 143-154.  DOI: 10.1016/j.rsci.2022.01.003 Abstract ( )   HTML ( )   PDF (55735KB) ( )   Serine/threonine phosphatase calcineurin (CN) is a unique but confounding calcium/calmodulin- mediated enzyme, which is composed of a catalytic subunit A (CNA) and a regulatory subunit B (CNB). We cloned six transcripts for CNA named from NlCNA-X1 to NlCNA-X6, one CNB named NlCNB1 and one CNB homologous gene NlCNBH1 from Nilaparvata lugens. All of them are constitutively transcripted in various tissues and developmental stages. The primary structure of the six isoforms showed obvious differences in the length and composition of the amino acid sequence between the two binding domains of Ca2+/calmodulin (CaM) and CNB. Ca2+-binding EF-hand motifs were found in NlCNB1 and NlCNBH1. The specific gene silencing of NlCNA, NlCNB1 and NlCNBH1 respectively by RNAi resulted in drastical reduction in survival rate, female weight, eclosion rate and fecundity of N. lugens. These results showed that NlCNA, NlCNB1 and NlCNBH1 were required for N. lugens growth and reproduction. The negative effects of NlCNB1 silence on nymph mortality (97%), molting malformation (90%) and female sterile (50%) were more serious than those of NlCNA or NlCNBH1. qRT-PCR and enzyme-linked immunosorbent assay (ELISA) analyses indicated that the nymphs with silenced NlCNA, NlCNB1 or NlCNBH1 showed impaired hormone and energy metabolism. In nymphs, the contents of 20-hydroxyecdysone (20E) after NlCNB1 RNAi and phenoloxidase after NlCNA RNAi were particularly decreased. These results suggested that NlCNA is involved in immunity of N. lugens by regulation of phenoloxidase, while NlCNB1 may control the growth and development of N. lugens by 20E signaling pathway in addition to interact with CNA. Injection of 70 ng/μL dsNlCNB1 resulted in 77.0% down regulation of NlCNB1, and the nymph mortality was up to 57.9% at 10 d after injection. Therefore, NlCNB1 could be a potential candidate target used for strategy design in control of N. lugens. Our results revealed the importance of CN in the regulation of the growth and development of N. lugens, which provided a basis for further study of the molecular mechanism of CN.

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Comparisons of Metabolic Profiles for Carbohydrates, Amino Acids, Lipids, Fragrance and Flavones During Grain Development in indica Rice Cultivars Chen Yibo, Wang Zhidong, Wang Chongrong, Li Hong, Huang Daoqiang, Zhou Degui, Zhao Lei, Pan Yangyang, Gong Rong, Zhou Shaochuan 2022, 29(2): 155-165.  DOI: 10.1016/j.rsci.2022.01.004 Abstract ( )   HTML ( )   PDF (28999KB) ( )   We used a widely targeted metabolomics approach to examine the metabolic changes in three pedigreed indica cultivars (Meixiangzhan 2, Meisizhan and Qixinzhan), with different eating qualities, at 8, 15 and 30 d after flowering (DAF) to explore the formation mechanism of rice eating and nutritional qualities at a global metabolic level. A total of 623 metabolites were identified, and results showed that metabolic variations among rice cultivars decreased with grain developmental stage, suggesting that sufficient carbohydrate and amino acid supply during grain development may contribute to excellent rice eating and nutritional quality formation. Lysophosphatidylcholines 19:0 and 16:1 were beneficial for excellent eating quality formation during grain development. Rice fragrance was attributed mainly to spermidine and γ-aminobutyric acid. Rice cultivars with excellent eating quality at 15-30 DAF had relatively higher flavone content, possibly because they had adequate carbohydrate and amino acid contents during grain development. These results provided insight into the mechanisms for establishing rice eating and nutritional qualities during grain formation at a global metabolic level, and can be applied towards improving rice quality.

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Functions of Nitrogen, Phosphorus and Potassium in Energy Status and Their Influences on Rice Growth and Development Ma Jiaying, Chen Tingting, Lin Jie, Fu Weimeng, Feng Baohua, Li Guangyan, Li Hubo, Li Juncai, Wu Zhihai, Tao Longxing, Fu Guanfu 2022, 29(2): 166-178.  DOI: 10.1016/j.rsci.2022.01.005 Abstract ( )   HTML ( )   PDF (27851KB) ( )   Nitrogen (N), phosphorus (P) and potassium (K) are important essential nutrients for plant growth and development, but their functions in energy status remains unclear. Here, we grew Nipponbare rice seedlings in a growth chamber for 20 d at 30 ºC/24 ºC (day/night) under natural sunlight conditions with different nutrient regimes. The results showed that N had the strongest influence on the plant growth and development, followed by P and K. The highest nonstructural carbohydrate content, dry matter weight, net photosynthetic rate (Pn), ATP content, as well as NADH dehydrogenase, cytochrome oxidase and ATPase activities were found in the plants that received sufficient N, P and K. The lowest values of these parameters were detected in the N-deficient plants. Higher dry matter accumulation was observed in the K-deficient than in the P-deficient treatments, but there was no significant difference in the ratio of respiration rate to Pn between these two treatments, suggesting that differences in energy production efficiency may have accounted for this result. This hypothesis was confirmed by higher ATP contents and activities of NADH dehydrogenase, cytochrome oxidase and ATPase in the K-deficient plants than in the P-deficient plants. We therefore inferred different abilities in energy production efficiency among N, P and K in rice seedlings, which determined rice plant growth and development.

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Pectin Methylesterases Enhance Root Cell Wall Phosphorus Remobilization in Rice Wu Qi, Tao Ye, Zhang Xiaolong, Dong Xiaoying, Xia Jixing, Shen Renfang, Zhu Xiaofang 2022, 29(2): 179-188.  DOI: 10.1016/j.rsci.2022.01.006 Abstract ( )   HTML ( )   PDF (26685KB) ( )   Pectin contributes greatly to cell wall phosphorus (P) remobilization. However, it is currently unclear whether the methylesterification degree of the pectin, which is related to the activity of pectin methylesterases (PMEs), is also involved in this process. Here, we demonstrated that elevated PME activity can facilitate the remobilization of P deposited in the cell wall. P-deficient conditions resulted in the reduction of root cell wall P content. This reduction was more pronounced in Nipponbare than in Kasalath, in company with a significant increment of the PME activity, indicating a possible relationship between elevated PME activity and cell wall P remobilization. This hypothesis was supported by in vitro experiments, as pectin with lower methylesterification degree had higher ability to release inorganic P (Pi) from insoluble FePO4. Furthermore, among the 35 OsPME members in rice, only the expression of OsPME14 showed a relationship with PME activity. In addition, transgenic rice lines overexpressing OsPME14 had increased PME activity, released more P from the root cell wall, and more resistant to P deficiency. In conclusion, PMEs enhance P remobilization in P-starved rice by increasing PME activity in Nipponbare, which in turn helps to remobilize P from the cell wall, and thus makes more available P.

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Epoxiconazole Improved Photosynthesis, Yield Formation, Grain Quality and 2-Acetyl-1-Pyrroline Biosynthesis of Fragrant Rice Luo Haowen, He Longxin, Du Bin, Pan Shenggang, Mo Zhaowen, Yang Shuying, Zou Yingbin, Tang Xiangru 2022, 29(2): 189-196.  DOI: 10.1016/j.rsci.2022.01.007 Abstract ( )   HTML ( )   PDF (25998KB) ( )   Epoxiconazole is a triazole compound. However, the effects of epoxiconazole on crop productivity and quality were rarely reported. In this study, we investigated the effects of epoxiconazole application on yield formation, grain quality attributes, and 2-acetyl-1-pyrroline (2-AP) content in fragrant rice. A three-year field experiment was carried out with a fragrant rice variety, Meixiangzhan 2. At the heading stage, 0, 0.02, 0.04, 0.08, 0.16 and 0.32 g/L epoxiconazole solutions were foliar applied to fragrant rice plants, respectively. The results showed that epoxiconazole application significantly increased grain yield, seed-setting rate and 1000-grain weight. Chlorophyll content and net photosynthetic rate of fragrant rice during the grain-filling stage significantly increased due to epoxiconazole application. Foliar application of epoxiconazole at 0.08 g/L increased grain protein content and decreased both chalky rice rate and chalkiness area ratio of fragrant rice. Epoxiconazole also substantially increased grain 2-AP content by inducing the regulation in contents of related synthetic precursors, including proline, pyrroline-5- carboxylic acid, ∆1-pyrroline and methylglyoxal. Overall, foliar application of epoxiconazole could be used for the improvement in grain yield, grain quality and 2-AP content in fragrant rice production when applied concentration at 0.08-0.32 g/L. Our findings provided the new roles of epoxiconazole in crop production.