Rice Science

Salt Tolerance in Rice: Focus on Mechanisms and Approaches

Naga Bheema Lingeswara Reddy Inja, Kim Beom-Ki, Yoon In-Sun, Kim Kyung-Hwan, Kwon Taek-Ryoun

2017, 24(3): 123-144. DOI: 10.1016/j.rsci.2016.09.00

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Salt tolerance is an important constrain for rice, which is generally categorized as a typical glycophyte. Soil salinity is one of the major constraints affecting rice production worldwide, especially in the coastal areas. Susceptibility or tolerance of rice plants to high salinity is a coordinated action of multiple stress responsive genes, which also interacts with other components of stress signal transduction pathways. Salt tolerant varieties can be produced by marker-assisted selection or genetic engineering by introducing salt-tolerance genes. In this review, we have updated on mechanisms and genes which can help in transferring of the salt tolerance into high-yielding rice varieties. We have focused on the need for integrating phenotyping, genomics, metabolic profiling and phenomics into transgenic and breeding approaches to develop high-yielding as well as salt tolerant rice varieties.

Population Structure and Marker-Trait Association in Indigenous Aromatic Rice

Rekha Talukdar Preeti, Rathi Sunayana, Pathak Khanin, Kumar Chetia Sanjay, Nath Sarma Ramendra

2017, 24(3): 145-154. DOI: 10.1016/j.rsci.2016.08.009

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Joha rice of Assam is a class of rice with aroma, good cooking qualities and excellent palatability, which are grown in different places of Assam with their adaptability to local situations. A total of 143 simple sequence repeat markers were used in this study to reveal sufficient genetic variations among the 40 Joha and 14 non-Joha rice genotypes. Polymorphism information content of these markers were from 0.17 to 0.88, where the average of 3.7 alleles were observed. The model-based population assignment and dendrogram analysis identified three distinct groups in the 54 rice accessions, which established a clear identity of Joha accessions from the Basmati accessions, indicating high diversity and strong population structure in Joha rice. Furthermore, a total of 29 significant marker-trait associations (P < 0.05) for 10 characters were detected. The QTLs related with yield and grain quality can be used effectively in crop improvement programs and for further fine mapping and validation of specific genes to develop gene-based perfect markers in rice breeding and for mining of better alleles of these genes in Joha rice collections.

Antioxidant Defense Mechanisms of Salinity Tolerance in Rice Genotypes

Golam Kibria Mohammad, Hossain Mahmud, Murata Yoshiyuki, Anamul Hoque Md

2017, 24(3): 155-162. DOI: 10.1016/j.rsci.2017.05.001

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In order to elucidate the role of antioxidant responses in salinity tolerance in rice genotypes under salt stress, experiments were conducted using four rice varieties, including salt-sensitive BRRI dhan 28 and three salt-tolerant varieties BRRI dhan 47, BINA dhan 8 and BINA dhan 10. Thirty-day-old rice seedlings were transplanted into pots. At the active tillering stage (35 d after transplanting), plants were exposed to different salinity levels (0, 20, 40 and 60 mmol/L NaCl). Salt stress caused a significant reduction in growth for all the rice genotypes. Growth reduction was higher in the salt-sensitive genotype than in the salt-tolerant ones, and BINA dhan 10 showed higher salt tolerance in all measured physiological parameters. The reduction in shoot and root biomass was found to be minimal in BINA dhan 10. Chlorophyll content significantly decreased under salt stress except for BINA dhan 10. Proline content significantly increased in salt-tolerant rice genotypes with increased salt concentration, and the highest proline content was obtained from BINA dhan 10 under salt stress. Catalase and ascorbate peroxidase activities significantly decreased in salt-sensitive genotype whereas significantly increased in salt-tolerant ones with increasing salt concentration. However, salt stress significantly decreased guaiacol peroxidase activity in all the rice genotypes irrespective of salt tolerance. K⁺/Na⁺ ratio also significantly decreased in shoots and roots of all the rice genotypes. The salt-tolerant genotype BINA dhan 10 maintained higher levels of chlorophyll and proline contents as well as catalase and ascorbate peroxidase activities under salt stress, thus, this might be the underlying mechanism for salt tolerance.

Expression Analysis of Genes Related to Rice Resistance Against Brown Planthopper, Nilaparvata lugens

Jannoey Panatda, Channei Duangdao, Kotcharerk Jate, Pongprasert Weerathep, Nomura Mika

2017, 24(3): 163-172. DOI: 10.1016/j.rsci.2016.10.001

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Brown planthopper (BPH) is an insect species that feeds on the vascular system of rice plants. To examine the defence mechanism of rice plants against BPH, the pathogenesis-related genes (PR1a, PR2, PR3, PR4, PR6, PR9, PR10a, PR13, PR15 and PRpha), signaling molecule synthesis genes (AOS, AXR, ACO and LOX), antioxidant-related genes (CAT, TRX, GST and SOD) and lignin biosynthesis-related genes (CHS, CHI and C4H) were investigated in a resistant rice variety. AOS, PR6, PR9 and PR15 genes showed significantly increased relative expression levels at 24.38-, 19.17-, 14.71-, and 12.74-fold compared to the control. Moderate increased relative expression levels of lignin biosynthesis-related gene (C4H), pathogenesis-related genes (PR4, PR10a and PRpha), and antioxidant-related gene (GST) were found, while CHI, LOX, SOD, TRX1 and AXR showed decreased relative expression levels. It was thus clearly shown that wound-induced response genes were activated in rice plants after BPH attacks through AOS activation. Jasmonic acid signaling molecule may activate PR6, PR15, GST and CAT subsequently increasing their expression for H₂O₂ detoxification. PR6 were expressed at the highest relative level among the PR genes. These genes therefore have also a considerable synergistic role with the other genes against BPH by interfered their digestion tract system.

Evaluation of Genotype × Environment Interaction in Rice Based on AMMI Model in Iran

Sharifi Peyman, Aminpanah Hashem, Erfani Rahman, Mohaddesi Ali, Abbasian Abouzar

2017, 24(3): 173-180. DOI: 10.1016/j.rsci.2017.02.001

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Identification of high-yielding stable promising rice lines and determination of suitable areas for rice lines would be done by additive main effects and multiplicative interaction (AMMI) model. Seven promising rice genotypes plus two check varieties Shiroudi and 843 were analyzed using a randomized complete block design with three replications in three consecutive years (2012, 2013 and 2014). Homogenous error variance was indicated in the nine environments for grain yield. The combined analysis of variance indicated significant effects of environment, genotype and genotype × environment (GE) interactions on grain yield. The significant effect of GE interaction reflected on the differential response of genotypes in various environments and demonstrated that GE interaction had remarkable effect on genotypic performance in different environments. The application of AMMI model for partitioning the GE interaction effects showed that only the first two terms of AMMI were significant based on Gollob’s F-test. The lowest AMMI-1 was observed for G7, G2 and G6. G7 and G6 had higher grain yield. According to the first eigenvalue, which benefits only the first interaction principal component scores, G1, G6, G2 and G9 were the most stable genotypes. The values of the sum of first two interaction principal component scores could be useful in identifying genotype stability, and G6, G5 and G2 were the most dynamic stable genotypes. AMMI stability value introduced G6 as the most stable one. According to AMMI biplot view, G6 was high yielding and highly stable genotype. In conclusion, this study revealed that GE interactions were an important source of rice yield variation, and its AMMI biplots were forceful for visualizing the response of genotypes to environments.

In planta Agrobacterium-Mediated Transformation of Rice

Ratanasut Kumrop, Rod-In Weerawan, Sujipuli Kawee

2017, 24(3): 181-186. DOI: 10.1016/j.rsci.2016.11.001

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The floral-dip transformation, the simplest technique, is no requirement of tissue culture procedure, and can directly transfer the interest gene into plant reproductive cells. It has been successfully applied to various plant species. In this study, the optimal conditions of a floral-dip method for production of transgenic rice variety RD41 were explored. The simple and effective inoculation medium was composed of Murashige and Skoog (MS) medium, 5% sucrose, 44 nmol/L benzylaminopurine, and 0.075% surfactant Tween-20 with pH 5.7. The transformation efficiencies of Agrobacterium tumefaciens strains AGL1 and EHA105 were compared with the Agrobacterium density at OD₆₀₀ = 0.8-1.0 and the co-cultivation at 25 ºC for 48 h. A. tumefaciens strain EHA105 gave slightly higher transformation efficiency than AGL1, with statistically non-significant difference. The floral-drop transformation using the optimal floral-dip conditions showed higher transformation efficiency than the floral-dip method, but the dropped flowers turned brown and died within 2 d. Production of transgenic rice variety RD41 by the floral-dip method was achieved using A. tumefaciens strain EHA105 with the optimal conditions. Screening for the gusA gene by PCR using the gusA specific primers in the T₀ lines, there were 4 transgenic lines from 286 T₀ lines (1.4% transformation efficiency). However, histochemical glucuronidase (GUS) assay demonstrated that only three of four transgenic lines exhibited gusA expression. These results indicated that floral-dip transformation is a potential tool for production of the transgenic rice, which can be used for molecular breeding via genetic engineering in the future.

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