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28 March 2020, Volume 27 Issue 2 Previous Issue    Next Issue
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Morphological Characteristics and Seed Physiochemical Properties of Two Giant Embryo Mutants in Rice Long Zhang, Ning Li, Huimin Fang, Linglong Zhao, Ke Guo, Jing Zhang, Qiaoquan Liu, Ling Jiang, Cunxu Wei 2020, 27(2): 81-85.  DOI: 10.1016/j.rsci.2019.04.006 Abstract ( )   HTML ( )   PDF (1326KB) ( )

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Rice Aroma: A Natural Gift Comes with Price and the Way Forward Hossain Prodhan Zakaria, Qingyao Shu 2020, 27(2): 86-100.  DOI: 10.1016/j.rsci.2020.01.001 Abstract ( )   HTML ( )   PDF (1183KB) ( )   Aromatic rice belongs to a small but important sub-group of rice, which is highly regarded for its excellent aroma and superior grain quality. Aromatic rice, especially Basmati- and Jasmine-type rice, is being traded at a high price in the local and global markets. Genetically, rice aroma is a phenotypical expression of spontaneous recessive mutations of the OsBadh2 gene (also known as fgr / badh2 / osbadh2 / os2AP gene). These mutations inhibit the flow of γ-aminobutyraldehyde (GAB-ald) to γ-aminobutyric acid (GABA), and consequently, the accumulated GAB-ald is diverted to a potent flavour component 2-acetyl-1-pyrroline (2AP) by a non-enzymatic reaction with methylglyoxal. The natural incidence of non-functional osbadh2 mutation along with selection and nursing by the farmer from the ancient time makes rice aroma as a prominent natural gift. As GABA and methylglyoxal play significant roles in stress tolerance, and their biosynthesis is strictly regulated in rice plants, the accumulation of 2AP in aromatic rice depends on the interaction of various genetic and environmental factors, and its production may come at some costs of sacrificing tolerance. This review focused on some potential underlying genes in the 2AP and GABA biosynthesis pathways, and analyzed most aspects of aroma formation in rice, and summarized the molecular mechanism of aroma production together with its genetic and non-genetic influencing factors. The present review also stated approaches to produce high-quality aromatic rice via developing novel cultivars and with good agronomic knowledge-based practice.

Research Paper

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Comprehensive Characteristics of MicroRNA Expression Profile Conferring to Rhizoctonia solani in Rice Wenlei Cao, Xinxin Cao, Jianhua Zhao, Zhaoyang Zhang, Zhiming Feng, Shouqiang Ouyang, Shimin Zuo 2020, 27(2): 101-112.  DOI: 10.1016/j.rsci.2019.04.007 Abstract ( )   HTML ( )   PDF (857KB) ( )   MicroRNAs (miRNAs) are about 22 nucleotides regulatory non-coding RNAs that play versatile roles in reprogramming plant responses to biotic and abiotic stresses. However, it remains unknown whether miRNAs confer the resistance to necrotrophic fungus Rhizoctonia solani in rice. To investigate whether miRNAs regulate the resistance to R. solani, we constructed 12 small RNA libraries from susceptible and resistant rice cultivars treated with water/pathogen at 5 h post inoculation (hpi), 10 hpi and 20 hpi, respectively. By taking the advantage of next-generation sequencing, we totally collected 400-450 known miRNAs and 450-620 novel miRNAs from the libraries. Expression analysis of miRNAs demonstrated different patterns for known and novel miRNAs upon R. solani challenge. Thirty-four miRNA families were identified to be expressed specifically in rice, and most of them were involved in plant disease resistance. A particular Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis result revealed that a great majority of target genes of regulated miRNAs belonged to the pathway of plant-pathogen interaction. Moreover, miR444b.2, miR531a, mir1861i, novel_miR1956 and novel_miR135 conferred response to R. solani infection confirmed by Northern blot. Our global understanding of miRNA profiling revealed that the regulation of miRNAs may be implicated in the control of rice immunity to R. solani. Analysis of the expression of miRNAs will offer the community with a direction to generate appropriate strategies for controlling rice sheath blight disease.

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Marker-Assisted Introgression of Quantitative Resistance Gene pi21 Confers Broad Spectrum Resistance to Rice Blast B. ANGELES-SHIM Rosalyn, P. REYES Vincent, M. del VALLE Marilyn, S. LAPIS Ruby, SHIM Junghyun, SUNOHARA Hidehiko, K. JENA Kshirod, ASHIKARI Motoyuki, DOI Kazuyuki 2020, 27(2): 113-123.  DOI: 10.1016/j.rsci.2020.01.002 Abstract ( )   HTML ( )   PDF (887KB) ( )   The quantitative resistance gene pi21 from Sensho was introgressed to an indica breeding line IR63307-4B-13-2, a pyramiding line IRBB4/5/13/21, and a tropical japonica line Kinandang Patong by marker-assisted backcrossing. A total of 192 improved lines at the BC4F3 and BC4F4 generations were developed and confirmed to have the gene introgression via genotyping using a pi21-specific InDel marker. Thirteen randomly selected improved lines, representing all the three genetic backgrounds, demonstrated resistance against leaf blast composites in the field and a broader spectrum resistance against individual isolates compared to the recurrent parents in the glasshouse. Specifically, the tested lines exhibited pi21-acquired resistance against 11 leaf blast isolates that elicited susceptible reactions from the recurrent parents. All the tested lines maintained a comparative heading date, and similar or improved panicle length, number of primary branches per panicle and number of total grains per panicle relative to the recurrent parents. The physical grain characteristics of the recurrent parents were also maintained in the 13 lines tested, although variability in the amylose content and chalkiness degree was observed. The successful marker-assisted introgression of pi21 in diverse genetic backgrounds and the resulting broader spectrum resistance of improved lines against leaf blast indicate the potential of pi21 for deployment in cultivars grown across other rice growing regions in Asia.

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Genetic Relationship and Structure Analysis of Root Growth Angle for Improvement of Drought Avoidance in Early and Mid-Early Maturing Rice Genotypes Pandit Elssa, Kumar Panda Rajendra, Sahoo Auromeera, Ranjan Pani Dipti, Kumar Pradhan Sharat 2020, 27(2): 124-132.  DOI: 10.1016/j.rsci.2020.01.003 Abstract ( )   HTML ( )   PDF (730KB) ( )   Deeper rooting 1 (Dro1) and Deeper rooting 2 (Dro2) are the QTLs that contribute considerably to root growth angle assisting in deeper rooting of rice plant. In the present study, a set of 348 genotypes were shortlisted from rice germplasm based on root angle study. Screening results of the germplasm lines under drought stress identified 25 drought tolerant donor lines based on leaf rolling, leaf drying, spikelet fertility and single plant yield. A panel containing 101 genotypes was constituted based on screening results and genotyped using Dro1 and Dro2 markers. Structure software categorized the genotypes into four sub-populations with different fixation index values for root growth angle. The clustering analysis and principal coordinate analysis could differentiate the genotypes with or without deeper rooting trait. The dendrogram constructed based on the molecular screening for deep rooting QTLs showed clear distinction between the rainfed upland cultivars and irrigated genotypes. Eleven genotypes, namely Dular, Tepiboro, Surjamukhi, Bamawpyan, N22, Dinorado, Karni, Kusuma, Bowdel, Lalsankari and Laxmikajal, possessed both the QTLs, whereas 67 genotypes possessed only Dro1. The average angle of Dro positive genotypes ranged from 82.7º to 89.7º. These genotypes possessing the deeper rooting QTLs can be taken as donor lines to be used in marker-assisted breeding programs.

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OsSRK1, an Atypical S-Receptor-Like Kinase Positively Regulates Leaf Width and Salt Tolerance in Rice Jinjun Zhou, Peina Ju, Fang Zhang, Chongke Zheng, Bo Bai, Yaping Li, Haifeng Wang, Fan Chen, Xianzhi Xie 2020, 27(2): 133-142.  DOI: 10.1016/j.rsci.2020.01.004 Abstract ( )   HTML ( )   PDF (969KB) ( )   Receptor-like kinases (RLKs) are important for plant growth, development and defense responses. The S-receptor protein kinases (SRKs), which represent an RLK subfamily, control the self- incompatibility among Brassica species. However, little information is available regarding SRK functions in rice. We identified a gene OsSRK1 encoding an atypical SRK. The transcript of OsSRK1 was induced by abscisic acid (ABA), salt and polyethylene glycol. OsSRK1 localized to the plasma membrane and cytoplasm. Leaf width was increased in OsSRK1-overexpression (OsSRK1-OX) transgenic rice plants, likely because of an increase in cell number per leaf. Furthermore, the expression levels of OsCYCA3-1 and OsCYCD2-1, which encode positive regulators of cell division, were up-regulated in leaf primordium of OsSRK1-OX rice plants relative to those in wild type. Meanwhile, the expression level of OsKRP1, which encodes cell cycle inhibitor, was down-regulated in the OsSRK1-OX plants. Therefore, it is deduced that OsSRK1 regulates leaf width by promoting cell division in the leaf primordium. Additionally, OsSRK1-OX plants exhibited enhanced ABA sensitivity and salt tolerance compared with wild type. These results suggest that OsSRK1 plays important roles in leaf development and salt responses in rice.

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Rice Heavy Metal P-type ATPase OsHMA6 Is Likely a Copper Efflux Protein Wenli Zou, Chang Li, Yajun Zhu, Jingguang Chen, Haohua He, Guoyou Ye 2020, 27(2): 143-151.  DOI: 10.1016/j.rsci.2020.01.005 Abstract ( )   HTML ( )   PDF (797KB) ( )   P1B-type heavy metal ATPases (HMAs) are transmembrane metal-transporting proteins that play a key role in metal homeostasis. We here reported the characterization of rice OsHMA6, a member of the P1B-type ATPase family. Phylogenetic tree analysis showed that OsHMA6 belonged to the Cu/Ag subgroup of the HMA family and had a close evolutionary relationship with OsHMA9. Amino acid sequence alignment showed 82.78% consistency between OsHMA6 and OsHMA9. OsHMA6 expressed in all organs at different growth stages, including spikelet, and abundant in leaf blades, however, OsHMA9 most strongly expressed in roots, but very low in spikelet. Excessive Cu2+ can up-regulate the expression of OsHMA6 and OsHMA9 in rice seedlings. The heterologous expression in yeast showed that OsHMA6 can significantly rescue the growth of yeast strain CM52 when supplied with 3 or 6 mmol/L Cu2+. Compared with the empty vector pYES2, the Cu concentration in OsHMA6-pYES2 decreased by 23.4% and 30.3% under 3 or 6 mmol/L Cu2+, respectively. Subcellular localization revealed that OsHMA6 was located in the plasma membrane. These results suggested that OsHMA6, similar to OsHMA9, is likely a copper efflux protein located in the plasma membrane.

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Expression Profiles and Protein Complexes of Starch Biosynthetic Enzymes from White-Core and Waxy Mutants Induced from High Amylose Indica Rice Yaling Chen, Yuehan Pang, Jinsong Bao 2020, 27(2): 152-161.  DOI: 10.1016/j.rsci.2020.01.006 Abstract ( )   HTML ( )   PDF (1105KB) ( )   Physicochemical properties of endosperm starches in milled rice determine its cooking and eating quality. Amylose is synthesized by granule-bound starch synthase I (GBSSI), whilst amylopectin is synthesized by the synergistic activities of starch synthases (SSs), branching enzymes (BEs) and debranching enzymes (DBEs). However, the complexes formed by starch biosynthetic enzymes are not well characterized. Gene expression profiles and protein complexes were determined in white-core (GM645) and waxy (GM077) mutants derived from a high amylose indica rice Guangluai 4 (GLA4). In GM645, genes including AGPS1, GBSSI, SSIIa, BEI, BEIIa, BEIIb, PUL, ISA1 and SP were significantly downregulated during seed development. In GM077, the expression levels of AGPL2, AGPS1, AGPS2b, SSIIIa, BEI, PUL and ISA1 were significantly upregulated. Co-immunoprecipitation assays revealed interactions of SSs-BEs, SSs-PUL and BEs-PUL in developing seeds. However, weak SSI-SSIIa interaction was detected in GM077, whilst SSI-PUL interaction was absent. Weak interaction signals for SSI-SSIIa, SSIIa-BEI, SSIIa-BEIIb, BEI-BEIIb and SSI-BEI were also observed in GM645. These results suggest that the protein-protein interactions for starch biosynthesis are modified in mutants, which provides insight into the mechanisms of starch biosynthesis, particularly in indica rice.

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Rhizosphere Aeration Improves Nitrogen Transformation in Soil, and Nitrogen Absorption and Accumulation in Rice Plants Chunmei Xu, Liping Chen, Song Chen, Guang Chu, Danying Wang, Xiufu Zhang 2020, 27(2): 162-174.  DOI: 10.1016/j.rsci.2020.01.007 Abstract ( )   HTML ( )   PDF (1231KB) ( )   Two rice cultivars (Xiushui 09 and Chunyou 84) were used to evaluate the effects of various soil oxygen (O2) conditions on soil nitrogen (N) transformation, absorption and accumulation in rice plants. The treatments were continuous flooding (CF), continuous flooding and aeration (CFA), and alternate wetting and drying (AWD). The results showed that the AWD and CFA treatments improved soil N transformation, rice growth, and N absorption and accumulation. Soil NO3- content, nitrification activity and ammonia-oxidising bacteria abundance, leaf area, nitrate reductase activity, and N absorption and accumulation in rice all increased in both cultivars. However, soil microbial biomass carbon and pH did not significantly change during the whole period of rice growth. Correlation analysis revealed a significant positive correlation between the nitrification activity and ammonia-oxidising bacteria abundance, and both of them significantly increased as the total N accumulation in rice increased. Our results indicated that improved soil O2 conditions led to changing soil N cycling and contributed to increases in N absorption and accumulation by rice in paddy fields.