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28 March 2021, Volume 28 Issue 2 Previous Issue    Next Issue
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High-Quality de novo Genome Assembly of Huajingxian 74, a Receptor Parent of Single Segment Substitution Lines Fangping Li, Yanhao Gao, Bingqi Wu, Qingpei Cai, Pengling Zhan, Weifeng Yang, Wanxuan Shi, Xiaohua Li, Zifeng Yang, Quanya Tan, Xin Luan, Guiquan Zhang, Shaokui Wang 2021, 28(2): 109-113.  DOI: 10.1016/j.rsci.2020.09.010 Abstract ( )   HTML ( )   PDF (12686KB) ( )

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Genetic Interaction of Hd1 with Ghd7, DTH8 and Hd2 Largely Determines Eco-Geographical Adaption of Rice Varieties in Southern China Zhenhua Zhang, Yujun Zhu, Shilin Wang, Yeyang Fan, Jieyun Zhuang 2021, 28(2): 114-118.  DOI: 10.1016/j.rsci.2021.01.001 Abstract ( )   HTML ( )   PDF (613KB) ( )

Review

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Drought Tolerance in Rice: Focus on Recent Mechanisms and Approaches Panda Debabrata, Sakambari Mishra Swati, Kumar Behera Prafulla 2021, 28(2): 119-132.  DOI: 10.1016/j.rsci.2021.01.002 Abstract ( )   HTML ( )   PDF (552KB) ( )   Drought stress is a serious limiting factor to rice production, which results in huge economic losses. It is becoming a more serious issue with respect to the global climate change. Keeping in view of the current and forecasted global food demand, it has become essential to enhance the crop productivity on the drought-prone rainfed lands with priority. In order to achieve the production target from rainfed areas, there is a requirement of rice varieties with drought tolerance, and genetic improvement for drought tolerant should be a high priority theme of research in the future. Breeding for drought tolerant rice varieties is a thought-provoking task because of the complex nature and multigenic control of drought tolerant traits would be a major bottleneck for the current research. A great progress has been made during last two decades in our understanding of the mechanisms involved in adaptation and tolerance to drought stress in rice. In this review, we highlighted the recent progresses in physiological, biochemical and molecular adaptation of rice to drought tolerance. A brief discussion on the molecular genetics and breeding approaches for drought tolerance in rice will be focused for the future crop improvement program for development of drought tolerant rice varieties.

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Genome Editing Strategies Towards Enhancement of Rice Disease Resistance Mishra Rukmini, Zheng Wei, Kumar Joshi Raj, Kaijun Zhao 2021, 28(2): 133-145.  DOI: 10.1016/j.rsci.2021.01.003 Abstract ( )   HTML ( )   PDF (815KB) ( )   The emerging pests and phytopathogens have reduced the crop yield and quality, which has threatened the global food security. Traditional breeding methods, molecular marker-based breeding approaches and use of genetically modified crops have played a crucial role in strengthening the food security worldwide. However, their usages in crop improvement have been highly limited due to multiple caveats. Genome editing tools like transcriptional activator-like effector nucleases and clustered regularly interspaced short palindromic repeats (CRISPR)-associated endonuclease Cas9 (CRISPR/Cas9) have effectively overcome limitations of the conventional breeding methods and are being widely accepted for improvement of crops. Among the genome editing tools, the CRISPR/Cas9 system has emerged as the most powerful tool of genome editing because of its efficiency, amicability, flexibility, low cost and adaptability. Accumulated evidences indicate that genome editing has great potential in improving the disease resistance in crop plants. In this review, we offered a brief introduction to the mechanisms of different genome editing systems and then discussed recent developments in CRISPR/Cas9 system-based genome editing towards enhancement of rice disease resistance by different strategies. This review also discussed the possible applications of recently developed genome editing approaches like CRISPR/Cas12a (formerly known as Cpf1) and base editors for enhancement of rice disease resistance.

Research Paper

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RAVL1 Activates IDD3 to Negatively Regulate Rice Resistance to Sheath Blight Disease Qian Sun, Shuo Yang, Xiaofan Guo, Siting Wang, Xintong Jia, Shuang Li, Yuanhu Xuan 2021, 28(2): 146-155.  DOI: 10.1016/j.rsci.2021.01.004 Abstract ( )   HTML ( )   PDF (1137KB) ( )   Sheath blight disease (ShB) has a severe impact on the production of rice. ABI3/VP1-like 1 (RAVL1) negatively regulated the rice defense mechanism against ShB, however, this regulatory mechanism is not clearly understood. In this study, we identified that indeterminate domain 3 (IDD3) was positively regulated by RAVL1. Further, chromatin immunoprecipitation (ChIP) assay, yeast one-hybrid assay and transient expression assay indicated a direct binding between RAVL1 and the IDD3 promoter region. IDD3 was ubiquitously expressed in different tissues and at different stages, and its expression was significantly enhanced by Rhizoctonia solani infection. IDD3 exhibited transcription activation activity in yeast and IDD3-GFP was found to be localized in the nucleus. IDD3 mutants exhibited no significant differences in response to ShB, while IDD3 overexpressors were more susceptible to ShB compared with wild type (WT) plants. Furthermore, IDD3 repressors were less susceptible to R. solani than WT plants. Interestingly, the expression of brassinosteroid-related genes (D2, D11 and BRI1) was lower in IDD3 repressors and higher in IDD3 overexpressors compared with WT. However, the ChIP assay revealed that IDD3 did not directly bind to the D2 and D11 promoters. Overexpression of IDD3 in BRI1 mutant d61-1 inhibited the activity of IDD3, reducing its susceptibility to ShB compared with IDD3 overexpressor and WT plants, indicating that IDD3 negatively regulated the rice defense mechanism against ShB by activating the BR signaling pathway. Thus, our analyses provided information to enhance the understanding of the rice defense mechanism against ShB.

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Osa-miR439 Negatively Regulates Rice Immunity Against Magnaporthe oryzae Junhua Lu, Xuemei Yang, Jinfeng Chen, Tingting Li, Zijin Hu, Ying Xie, Jinlu Li, Jiqun Zhao, Mei Pu, Hui Feng, Jing Fan, Yanyan Huang, Jiwei Zhang, Wenming Wang, Yan Li 2021, 28(2): 156-165.  DOI: 10.1016/j.rsci.2021.01.005 Abstract ( )   HTML ( )   PDF (1228KB) ( )   Osa-miR439 is a rice-specific microRNA family. Here we showed that Osa-miR439 acted as a negative regulator in rice immunity against blast fungus Magnaporthe oryzae. Osa-miR439 differentially responded to M. oryzae between susceptible and resistant rice accessions. The accumulation of Osa-miR439 was constitutively more in the susceptible accession than in the resistant one. Transgenic lines overexpressing Osa-miR439a (OX439a) showed higher susceptibility associating with lower induction of defense-related genes and less hydrogen peroxide (H2O2) accumulation at the infection sites than the control plants. In contrast, transgenic lines expressing a target mimic of Osa-miR439 (MIM439) displayed compromised susceptibility associating with increased H2O2 accumulation. Furthermore, we found that the expression of three predicted target genes was decreased in OX439a but increased in MIM439 in comparison to control plants, and this expression was differential in susceptible and resistant accessions upon M. oryzae infection, indicating that Osa-miR439a may regulate rice blast resistance via these genes. Our results unveiled the role of Osa-miR439a in rice blast resistance and provided the potentiality to improve the blast resistance via miRNA.

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Exogenous Peroxidase Mitigates Cadmium Toxicity, Enhances Rhizobial Population and Lowers Root Knot Formation in Rice Seedlings Singh Priyanka, Pokharia Chitra, Shah Kavita 2021, 28(2): 166-177.  DOI: 10.1016/j.rsci.2021.01.006 Abstract ( )   HTML ( )   PDF (1266KB) ( )   Soil cadmium (Cd) causes toxicity and oxidative stress, alters biochemical processes and root knot formation in rice. Irrigation of exogenous peroxidase (POX) together with its co-substrate H2O2 (POXRice + H2O2), is likely to have protective effect upon the biochemical and nodular changes in rice grown in Cd-rich soil. Exposure to Cd concentration of 1.00 mg/L increased oxidative stress, loss of cell viability, electrolyte leakage and root knot formation, whereas it significantly lowered the chlorophyll level and rhizobium growth in rice. Irrigation of exogenous POXRice + H2O2 to Cd-stressed rice seedlings reversed the Cd-induced alterations in rice to levels similar in control (non-stressed) seedlings. Results provided strong evidence of exogenous POXRice + H2O2-mediated reversal and restoration of physiological and biochemical processes as well as increased resistance of rice seedlings to root knot formation. Irrigation with POXRice + H2O2 appeared to contribute towards bringing normoxic conditions in the otherwise hypoxic soil environment by enhancing the O2 in pot-experiments due to reduced Cd uptake, enhanced mineral homeostasis of essential elements viz. P, Fe, Mo, Mg and Mn for maintenance of root architecture damaged by lipid peroxidation and reduction in oxidative stress by reducing Cd-induced reactive oxygen species generation. Therefore, the mitigation of Cd-toxicity in rice through this novel approach appeared to be a promising mode to limit Cd-uptake, modulate protective and tolerance mechanisms for sustainable rice yield in Cd-contaminated rice-croplands and prevent nematode attack in rice, however, more detailed studies are needed prior to large scale applications.

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Growth and Photosynthesis Responses of a Super Dwarf Rice Genotype to Shade and Nitrogen Supply Schmierer Marc, Knopf Oliver, Asch Folkard 2021, 28(2): 178-190.  DOI: 10.1016/j.rsci.2021.01.007 Abstract ( )   HTML ( )   PDF (1138KB) ( )   Specific aspects of plant cultivation require tests under fully controlled environmental conditions with restricted energy supply, such as orbit-based space laboratories and low-light conditions. For these growing conditions, super dwarf plants have been developed as model crops, and a gibberellin- deficient Super Dwarf Rice genotype was proposed as a model crop for space flight plant experiments. We tested this genotype in a climate chamber experiment under different illumination and nitrogen supply levels to assess its suitability under scenarios with limited resource availability. A 25% reduction in illumination led to a 75% reduction in yield, mainly due to a 60% reduction in formed tillers and 20% reduction in grain weight, and a 80% reduction in illumination caused total yield loss. Leaf area under reduced illumination was significantly lower, and only marginal changes in the dimensions of leaves were observed. Plant photosynthesis was not significantly different between control and 75% illumination. This was explained by a higher photochemical efficiency under lower light conditions and a reduced mesophyll resistance. Therefore, we concluded that this genotype is well-suited for plant experiments under space and light-limited conditions since it kept its small stature and showed no shade avoidance mechanisms, such as leaf elongation, which would complicate experiments under low-light conditions. Nitrogen concentrations of 2.8 and 1.4 mmol/L led to no differences in plant growth. We concluded that a nitrogen concentration of 1.4 mmol/L is sufficient for this genotype under the light intensities.

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Effects of Early- and Late-Sowing on Starch Accumulation and Associated Enzyme Activities During Grain Filling Stage in Rice Wenting Wang, Wenpei Cui, Ke Xu, Hui Gao, Haiyan Wei, Hongcheng Zhang 2021, 28(2): 191-199.  DOI: 10.1016/j.rsci.2021.01.008 Abstract ( )   HTML ( )   PDF (899KB) ( )   The environmental temperature occurring during the grain filling stage is an important factor affecting starch synthesis and accumulation in rice. We investigated starch accumulation, amylase activity and starch granule size distribution in two low-amylose japonica rice varieties, Nanjing 9108 and Fujing 1606, grown in the field at different filling temperatures by manipulating sowing date. The two rice varieties exhibited similar performances between two sowing dates. Total starch, amylose and amylopectin contents were lower at the early-filling stage of T1 treatment (Early-sowing) compared with those at the same stage in T2 treatment (Late-sowing). In contrast, at the late-filling stage, when field temperatures were generally decreasing, total starch and amylopectin contents in T1 were higher compared to those in T2. The ideal temperature for strong activity of ADP-glucose pyrophosphorylase and soluble starch synthase was about 22 ºC. A higher temperature from the heading to maturity stages in T1 increased the activities of starch branching enzyme and suppressed the activities of granule bound starch synthetase and starch debranching enzyme. We found that rice produced larger-sized starch granules under the T1 treatment. These results suggested that due to the early-sowing date, the high temperature (30 ºC) occurring at the early-filling stage hindered starch synthesis and accumulation, however, the lower temperatures (22 ºC) at the late-filling stage allowed starch synthesis and accumulation to return to normal levels.

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Lodging Resistance Related to Root Traits for Mechanized Wet-Seeding of Two Super Rice Cultivars Minghua Zhang, Zhaowen Mo, Juan Liao, Shenggang Pan, Xiongfei Chen, Le Zheng, Xiwen Luo, Zaiman Wang 2021, 28(2): 200-208.  DOI: 10.1016/j.rsci.2021.01.009 Abstract ( )   HTML ( )   PDF (616KB) ( )   Mechanical hill wet-seeded rice machine is beneficial for establishing and growing uniform rows of seedlings. However, there is limited knowledge regarding the effects of the establishment of furrows on growth, lodging and yield, and their relationships with root traits. In this study, field experiments were conducted during 2012 and 2013 using two super rice varieties (hybrid rice Peizataifeng and inbred rice Yuxiangyouzhan) under three furrow establishment treatments (T1, both water and seed furrows were established by the machine; T2, only seed furrows were established by the machine; and T3, neither water nor seed furrows were established by the machine). Lodging index, lodging-related traits, grain yield, above-ground dry weight and root traits were measured. The results showed that the lodging index was significantly affected by the treatments with furrows (T1 and T2). The strongest lodging resistance was detected in the mechanical hill wet-seeded rice with furrow treatment (T1) in both 2012 and 2013. Lodging resistance was strongly related to the breaking resistance. No significant difference was found in grain yield or dry weight of the mechanical hill wet-seeded rice. Therefore, the mechanical hill wet-seeded rice with furrow treatment increased rice lodging resistance, which was related to root traits.