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10 May 2021, Volume 35 Issue 3 Previous Issue    Next Issue
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Reviews and Special Topics

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Research Progress of Photoperiod Regulation in Rice Flowering Yubo WANG, Yue WANG, Xiong LIU, Wenbang TANG 2021, 35(3): 207-224.  DOI: 10.16819/j.1001-7216.2021.0514 Abstract ( )   HTML ( )   PDF (1690KB) ( )   As an important agronomic trait, heading date is determined by its own genetic factors and environmental factors, which has a great impact on the ecological adaptation area and yield factors of rice variety. In the past two decades, from the recognition of day length to the activation of flowering in the stem apex meristem, great progress has been made in the molecular regulation mechanism of rice photoperiod-induced flowering. A large number of regulatory genes related to flowering have been isolated and cloned, and integrated into the molecular network of photoperiod regulation. When plants are in favorable conditions, this network activates floral regulatory genes, promotes the expression of florigen gene, and transports florigen to the apical meristem, thus driving the development of meristem cells and forming flowers finally. In this paper, Arabidopsis thaliana is used as a reference to discuss the genetic variation of rice photoperiod regulation network and its extension from low latitude to high latitude so as to provide valuable information for the cultivation of ecological varieties and the molecular mechanism of photoperiod regulation.

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Research Progress on Cadmium Uptake and Its Transport and Accumulation Among Organs in Rice Bo FANG, Tengwei XIAO, Nana SU, Yan XIA, Zhenguo SHEN, Jin CUI 2021, 35(3): 225-237.  DOI: 10.16819/j.1001-7216.2021.0719 Abstract ( )   HTML ( )   PDF (29799KB) ( )   With deteriorating heavy metal pollution in soil and atmosphere, heavy metals contents in crops often exceeds the threshold. Heavy metals in soil are difficult to be degraded and are easily absorbed by plant roots and accumulated in crops. Heavy metals in atmosphere fall down on the surface of leaves and could enter into leaves through the stomata eventually, making their way into human body through the food chain and endangering human health. Rice is one of the most important food sources in China, and in some cases, cadmium content in rice exceeds the standard. Cadmium (Cd) is a non-essential element in rice and mainly enters rice root cells through other divalent ion channels. Besides, Cd can enter rice leaves by the adsorption and internalization of leaf cuticle and the permeation of stomatal. The transport of Cd in rice depends on the transporters of other metal ions. The uptake and distribution of Cd organs is a dynamic process, which is driven by transporters in roots, from root to shoot (xylem loading) and from source to sink in phloem (including seed loading). In this review, we elaborated the uptake of Cd from roots and leaves, the allocation of Cd among organs and the accumulation of Cd in rice grains. This review will lay a theoretical basis for reducing the content of Cd in rice grains and solving the problem about Cd pollution in some planting areas in South China.

Research Papers

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Location and Candidate Gene Analysis of Rice Clustered Spikelets Gene OsCL6 Wei LIU, Zhanhua LU, Dongbai LU, Xiaofei WANG, Shiguang WANG, Jia XUE, Xiuying HE 2021, 35(3): 238-248.  DOI: 10.16819/j.1001-7216.2021.0604 Abstract ( )   HTML ( )   PDF (29928KB) ( )   【Objective】The mapping and candidate gene analysis of rice clustered spikelet genes help clone the functional genes for clustered spikelet caused by shortening of the branch length in the process of panicle development. 【Method】A stable clustered spikelet mutant cl6 was obtained through the space mutation breeding technique with Yuenongsimiao, a good quality rice cultivar in Guangdong Province as material. F1 and F2 mapping populations were constructed by crossing cl6 with Yuejinyinzhan. The clustered spikelet gene was mapped and candidate genes were predicted and evaluated by combining with transcriptome sequencing. 【Result】Genetic analysis showed that the trait was controlled by a pair of semi-dominant gene. The gene was mapped to an interval about 416 kb on chromosome 6 by Bulked Segregant Analysis(BSA). Furthermore, OsFBK16 was selected as the best candidate gene through expression profiling analysis, RNA-seq, gene sequence differences analysis and qRT-PCR verification. A 9 bp insertion mutation in the 5'-UTR region of this gene suggests that it may regulate transcription or translation process through secondary structural changes and participating in the differentiation of stems during the development of young panicle of rice. 【Conclusion】It will lay a theoretical foundation for analyzing the shortening mechanism of secondary branches and spikelet peduncle length.

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Differences in Eating and Cooking Quality Traits of Semi-waxy japonica Rice Cultivars in Jiangsu Province Zheng TIAN, Chunfang ZHAO, Yadong ZHANG, Qingyong ZHAO, Zhen ZHU, Ling ZHAO, Tao CHEN, Shu YAO, Lihui ZHOU, Wenhua LIANG, Kai LU, Cailin WANG, Hongsheng ZHANG 2021, 35(3): 249-258.  DOI: 10.16819/j.1001-7216.2021.01103 Abstract ( )   HTML ( )   PDF (9354KB) ( )   【Objective】 In recent years, a large number of semi-waxy japonica rice varieties were bred in Jiangsu Province. It was found that there were great differences in ECQ (eating and cooking quality) and physicochemical characteristics among these varieties. Exploring the regulation mechanisms behind the ECQ of semi-waxy rice will provide useful information for rice breeding. 【Method】 In this study, 39 semi-waxy japonica rice varieties from Jiangsu Province Excellent Taste Rice Appraisal Conference were used as materials. By analyzing 24 ECQ related traits, such as taste properties, physicochemical characteristics, RVA spectrum parameters and textural properties, the differences and correlation among different taste value groups were found. 【Result】According to the taste value, these semi-waxy japonica rice varieties were divided into three groups, including the high taste value group (>80), the medium taste value group (70-80) and the low taste value group (<70). Compared with the low taste value group, the high taste value group showed lower chalky grain rate, PC (protein content), and hardness, and higher GC(gel consistency), viscosity and transparency, and better cooked rice appearance. However, AC (amylose content), PaT (Pasting temperature) and RVA values exhibited insignificant difference. The correlation analysis showed that the taste value of rice was significantly positively correlated with AC and GC, and significantly negatively correlated with PC, PaT, transparency and chalkiness. However, there was no significant correlation between each trait in the high taste value group. In the medium and low taste value groups, a significantly positive correlation was detected between AC and the taste value. 【Conclusion】The appearance and physicochemical qualities have important influences on the formation of the ECQ of semi-waxy japonica rice. Varieties with higher taste value tend to have better appearance quality and higher AC and GC, lower PC; thus these traits should be paid more attention in the process of semi-waxy rice breeding.

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Identification and Fine Mapping of a Grain Width Mutant gw4 in Rice Xuemei DENG, Peng HU, Yueying WANG, Yi WEN, Yiqing TAN, Hao WU, Kaixiong WU, Junge WANG, Linlin HOU, Lixin ZHU, Li ZHU, Guang CHEN, Dali ZENG, Guangheng ZHANG, Longbiao GUO, Zhenyu GAO, Deyong REN, Qian QIAN, Jiang HU 2021, 35(3): 259-268.  DOI: 10.16819/j.1001-7216.2021.01204 Abstract ( )   HTML ( )   PDF (34626KB) ( )   【Objective】Grain size is an important agronomic trait that determines yield and appearance quality in rice. Screening and identification of new grain size mutants will lay a foundation for further study of the regulation mechanism of grain development. 【Method】A grain width mutant gw4（grain width on chromosome 4）was obtained from 1% EMS mutagenized population of Zhonghua 11. The scanning electron microscope analysis of the outer and inner surfaces cells of glumes was carried out, and grain size and other agronomic traits were measured at the heading and maturity stages, respectively. With the map-based cloning, the mutant individuals derived from F2 population of gw4 and TN1 were used for fine mapping. The candidate gene was determined by gene sequencing based on bioinformatics analysis, and expression analysis of grain size-related genes was carried out by the RT-PCR. 【Result】Besides narrow grains, gw4 also showed decreased phenotype values in plant height, grain length, thousand grain weight, grain number, number of primary and secondary rachis branches. Scanning electron microscope observation presented that both cell length and width of inner and outer surfaces cells of glumes were smaller than the wild type. Genetic analysis showed that the narrow grain phenotype was regulated by a single recessive nuclear gene, which was fine mapped to a region of 31.74 kb between the two markers BS6 and EX49 on chromosome 4. Sequence analyses revealed a single base substitution of G to A was found in LOC_Os04g01590 which resulted in a substitution of glycine to aspartic acid, and RT-PCR analysis indicated that it was mainly expressed in young panicles with declined expression level in mutant as compared with the wild type. 【Conclusion】GW4 is mainly involved in grain width development, and its candidate gene should be LOC_Os04g01590, which lays a foundation for further perfecting the genetic regulatory network of grain size.

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Relationship Between Canopy Microclimate at Grain Filling Stage and Rice Quality of Directly Seeded Rice Under Water and Nitrogen Interaction Yunxia WU, Changchun GUO, Yongjian SUN, Fangyan LIU, Zhiyuan YANG, Yuanyuan SUN, Mingtian MA, Jun MA 2021, 35(3): 269-278.  DOI: 10.16819/j.1001-7216.2021.0314 Abstract ( )   HTML ( )   PDF (1506KB) ( )   【Objective】Field canopy microclimate is the most direct environment factor for rice growth and development. The management of water and nitrogen fertilizer affects the growth of rice and thus affect the canopy microclimate of paddy field. Studying the effect of water and nitrogen interaction on the canopy microclimate during the seed-filling stage and rice quality of directly seeded rice can enrich and improve water and nitrogen management of the directly seeded rice. 【Method】With hybrid rice F You 498 as material, three irrigation treatments were designed including flooding (W1), dry-wet alternate (W2) and drying (W3) as well as three N fertilizer application methods with basal fertilizer: fertilizer for tillering: topdressing for panicle initiation 5:3:2(N1), 3:3:4(N2) and 3:1:6(N3), The effect of water and nitrogen interaction on canopy temperature, light intensity and rice quality of directly-seeded rice were analyzed during grain filling stage. The relationship between canopy microclimate and rice quality was also discussed. 【Result】The results showed that irrigation mode and N fertilization interactions had a significant or extremely significant effect on milling quality, appearance quality, and cooking and palatability of directly seeded rice. Under the conditions of 150 kg/hm2 N application rate for each irrigation method, the most suitable panicle N-fertilizer level should account for 20% of total N. Coupled with W2, it can further improve rice quality. The ratio of N-fertilizer for panicle initiation increased to 60%, leading to the decrease of daily temperature difference, total temperature difference, accumulated temperature, effective accumulated temperature, daily average light intensity and rice quality of directly seeded rice under irrigation. Under the interaction of water and N, the canopy microclimate in the field exerted the greatest impact on milling quality, and cooking and palatability of directly seeded rice. The effect of temperature on the head milled rice rate was greater than the light intensity, and the effective accumulated temperature had the highest correlation with head milled rice rate. Light intensity was the most closely related to the appearance, taste and comprehensive score of rice cooking and palatability quality. 【Conclusion】It is preliminarily proved that the interaction between water and nitrogen affects rice quality by changing the microclimate of the direct-seeded rice canopy. The results will lay a theoretical and practical basis for improvement of the quality and yield of direct-seeded rice.

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Study on the Characteristics of Soft japonica Rice Varieties with Good Taste and High Yield in Taihu Lake Area Qing ZHANG, Yajie HU, Baowei GUO, Hongcheng ZHANG, Xiaojie XU, Yufeng XU, Banghui ZHU, Jiefen XU, Zhongyi NIU, Rongwen TU 2021, 35(3): 279-290.  DOI: 10.16819/j.1001-7216.2021.0907 Abstract ( )   HTML ( )   PDF (4251KB) ( )   【Objective】It is of significance to explore the characteristics of soft japonica rice varieties with good taste and high yield in Taihu Lake area.【Method】 Soft japonica rice varieties suitable for cultivation in Taihu Lake were collected. According to the growth duration, yield and taste quality of the rice varieties, the differences in yield and quality formation of soft japonica rice varieties at different ripening stages were compared. 【Result】Compared with the medium yield type, the number of grains per panicle and the number of spikelets of the high yield type significantly increased in the population. The number of panicle, grain number per panicle and seed setting rate of the good taste type were equal to those of the medium taste type, while the 1000-grain weight was lower. Compared with the medium yield type, the high yield type had higher dry matter accumulation and nitrogen accumulation in the middle and late growth stages, and the final dry matter weight and total nitrogen accumulation were higher. Compared with the medium taste type, brown rice rate, milling rice rate and head milling rice rate of good taste rice increased, chalky rice percentage and chalkiness degree increased significantly, amylose content and protein content reduced, gel consistency were longer, the peak viscosity, hot paste viscosity, breakdown, final viscosity increased, rice and eating value increased significantly. 【Conclusion】 The soft japonica rice varieties with good taste and high yield in Taihu Lake region were featured with large panicle, low grain weight, strong dry matter and nitrogen accumulation ability in middle and late growth stages, good processing quality, poor appearance quality, and excellent cooking and eating quality.

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Analysis on the Key Factors of Soil Physicochemical Properties Responsible for Changes in Rice Yield with Chinese Milk Vetch Turned over for Different Years Kailou LIU, Tianfu HAN, Wenjun LI, Xichu YU, Zhihua HU, Huicai YE, Dandan HU, Huijie SONG, Daming LI, Qinghai HUANG 2021, 35(3): 291-302.  DOI: 10.16819/j.1001-7216.2021.0402 Abstract ( )   HTML ( )   PDF (27705KB) ( )   【Objective】The Chinese milk vetch (Astragalus sinicus L.) is an important green manure in the winter fallow of double-cropping rice system. The long-term returning of Chinese milk vetch to the field could achieve both soil fertility improvement and higher rice yield. However, it is still unclear that the key factors among many soil physical and chemical indicators, which drives the change of rice yield in turnover of Chinese milk vetch for different years. 【Method】 Five treatments with 0, 3, 5, 10, and 15 (G0, G3, G5, G10, and G15) turnover years of Chinese milk vetch were selected in Yujiang District of Jiangxi Province, China, the traditional planting area of Chinese milk vetch. The soil aggregates, organic matter, nitrogen, phosphorus, potassium contents and soil acidification characteristics were analyzed. Furthermore, the relationship between soil indicators and yield of early rice was explored. 【Result】The proportions of > 2 mm aggregate in G5, G10 and G15 were significantly increased. The longer turnover years of Chinese milk vetch led to the higher contents of soil organic matter, total nitrogen and phosphorus, available nitrogen, phosphorus, potassium, and readily available potassium. Compared with G0, the soil pH values in G10 and G15 were increased by 0.83 and 0.65 units. Moreover, the contents of exchangeable acid, hydrogen, and aluminum in G15 were significantly decreased as compared with those in G0. The comparison of correlation coefficients indicated that the proportion of >2 mm aggregate, soil organic matter, available nitrogen had higher interrelation with the grain yield (R2> 0.80, P<0.01). In addition, it was found that the turnover years of Chinese milk vetch significantly affected the soil aggregates, organic matter, and nutrient indicators, leading to the change of rice yield. 【Conclusion】In the double-cropping rice system, long-term turnover of Chinese milk vetch could be the main pattern to achieve higher soil fertility and rice yield. The soil acidification can be alleviated when more than 10 years turnover of Chinese milk vetch. The macro-aggregate content was more sensitive to different turnover years of Chinese milk vetch. It suggested that soil organic matter and available nitrogen were the key factors to the change of rice yield.

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Different Reactions of Rice Monogenic Line IRBL9-W Harboring Pi9 Gene to Magnaporthe oryzae Containing AvrPi9 During Seedling and Adult-plant Stages Shufang LIU, Liying DONG, Xundong LI, Wumin ZHOU, Qinzhong YANG 2021, 35(3): 303-310.  DOI: 10.16819/j.1001-7216.2021.0717 Abstract ( )   HTML ( )   PDF (1295KB) ( )   【Objective】 The Pi9 gene confers broad-spectrum resistance against Magnaporthe oryzae. Rice monogenic line IRBL9-W carrying single blast resistance gene Pi9 is highly resistant to leaf blast during the seedling stage, but it is susceptible to neck blast at adult-plant stage in blast nursery. It is important to analyze the mechanism behind the reversion of resistance to Magnaporthe oryzae, which will provide important information for effective utilization of Pi9 in disease-resistant rice breeding program.【Method】Eight single spore strains of M. oryzae isolated from neck blast samples of diseased IRBL9-W, and one isolate Y363 were artificially inoculated by spraying at seedling stage to pathotype their pathogenicity on 24 monogenic lines including IRBL9-W. Two out of eight strains and control strain Y363 were further selected and inoculated on IRBL9-W at late-booting stage by injecting to evaluate their pathogenicity. The alleles of M. oryzae AvrPi9 gene cognate to rice blast resistance gene Pi9 were amplified and sequenced with AvrPi9-specific primers in nine strains. Total RNA of the rice monogenic line IRBL9-W in seedling and late-booting stage was extracted from young leaf and panicle, respectively. The expression analysis of Pi9 gene was performed by semi-quantitative RT-PCR and real-time qRT-PCR. 【Result】 The monogenic line IRBL9-W was completely resistant to the nine M. oryzae strains at the seedling stage exposed to the artificial spraying. However, IRBL9-W was susceptible to panicle blast when inoculated with both two randomly selected strains (YX2-7-1 and YX2-15-1) isolated from panicle blast lesions of IRBL9-W, and the control strain Y363 by injecting inoculation at the late-booting stage. Compared with AvrPi9, allelic sequence amplified from Y363 was identical to cloned AvrPi9, and the coding region of the other eight strains isolated from IRBL9-W panicle blast was identical to AvrPi9 gene, except for a 16-bp deletion at -264 bp upstream of the coding starting position in the eight strains. Given high resistance of IRBL9-W to these strains at the seedling stage, we contended that this 16-bp deletion did not affect the function of AvrPi9 gene; qRT-PCR results showed that the relative expression level of Pi9 gene in panicle was only 47.3% as compared to that in seedling leaves. 【Conclusion】Compared with the relative expression level of Pi9 gene at the seedling stage in IRBL9-W, the significant decrease of Pi9 gene expression level in panicle of IRBL9-W could be the cause of susceptibility to M. oryzae at late-booting stage.