Highly efficient protocol for callogenesis, somagenesis and regeneration of Indica rice plants

Callus induction and regeneration in high-altitude Himalayan rice genotype SR4 via seed explant

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In the present study, an efficient protocol for callusing and regeneration via direct and indirect means was established using mature seeds as source of explants as they are accessible round the year and receptive to transformation via callus.

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Highest frequency (96.6%) of callus induction was obtained in MS media containing 3.0 mg/L 2, 4-D.

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Highest regeneration frequency (100%) from callus was obtained from MS media supplemented with 5.0 mg/L BAP and 0.5 mg/L NAA with highest number of shoots having an average shoot length 9.14 ± 0.204 (cm) after four weeks of culture.

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Direct multiple shoot regeneration from seed explants was obtained using various concentrations of TDZ and BAP with highest regeneration frequency was observed in MS media supplemented with 6 mg/L of TDZ with maximum number of shoots.

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The present study is attempt to develop highly efficient regeneration protocol via both direct and indirect ways utilizing mature seeds as source explant and thus can be utilized for molecular studies for genetic advancement of Himalayan rice genotype SR4 through transformation.

SR4 genotype of rice is high altitude Himalayan rice prone to various abiotic stresses such as cold stress and therefore gives a poor yield. An efficient protocol for callusing and regeneration via direct and indirect means was established using mature seeds as an explant which can be utilized for molecular studies for genetic advancement of Himalayan rice genotype SR4 through transformation. Highest frequency (96.6%) of callus induction was obtained on MS media 3.0 mg/L 2, 4-D. While maximum regeneration frequency (100%), number of shoots with maximum length 9.14 ± 0.204 (cm) from callus was recovered from MS media amended with 5.0 mg/L BAP in combination with 0.5 mg/L NAA with highest number of shoots having an average shoot length 9.14 ± 0.204 (cm) after four weeks of culture. Direct multiple shoot regeneration from seed explants was obtained using various concentrations of TDZ and BAP with highest regeneration frequency was observed on MS media fortified with 6 mg/L of TDZ with maximum number of shoots. The shoots developed roots on MS media supplemented with 0.6 mg/L IBA.

Screening and Expression of a Silicon Transporter Gene (Lsi1) in Wild-Type Indica Rice Cultivars

Silicon (Si) is one of the most prevalent elements in the soil. It is beneficial for plant growth and development, and it contributes to plant defense against different stresses. The Lsi1 gene encodes a Si transporter that was identified in a mutant Japonica rice variety. This gene was not identified in fourteen Malaysian rice varieties during screening. Then, a mutant version of Lsi1 was substituted for the native version in the three most common Malaysian rice varieties, MR219, MR220, and MR276, to evaluate the function of the transgene. Real-time PCR was used to explore the differential expression of Lsi1 in the three transgenic rice varieties. Silicon concentrations in the roots and leaves of transgenic plants were significantly higher than in wild-type plants. Transgenic varieties showed significant increases in the activities of the enzymes SOD, POD, APX, and CAT; photosynthesis; and chlorophyll content; however, the highest chlorophyll A and B levels were observed in transgenic MR276. Transgenic varieties have shown a stronger root and leaf structure, as well as hairier roots, compared to the wild-type plants. This suggests that Lsi1 plays a key role in rice, increasing the absorption and accumulation of Si, then alters antioxidant activities, and improves morphological properties.

Over-Expression of the Pikh Gene with a CaMV 35S Promoter Leads to Improved Blast Disease (Magnaporthe oryzae) Tolerance in Rice

Magnaporthe oryzae is a rice blast fungus and plant pathogen that causes a serious rice disease and, therefore, poses a threat to the world's second most important food security crop. Plant transformation technology has become an adaptable system for cultivar improvement and to functionally analyze genes in plants. The objective of this study was to determine the effects (through over-expressing and using the CaMV 35S promoter) of Pikh on MR219 resistance because it is a rice variety that is susceptible to the blast fungus pathotype P7.2. Thus, a full DNA and coding DNA sequence (CDS) of the Pikh gene, 3172 bp, and 1206 bp in length, were obtained through amplifying the gDNA and cDNA template from a PH9-resistant rice variety using a specific primer. Agrobacterium-mediated transformation technology was also used to introduce the Pikh gene into the MR219 callus. Subsequently, transgenic plants were evaluated from the DNA to protein stages using polymerase chain reaction (PCR), semi-quantitative RT-PCR, real-time quantitative PCR and high performance liquid chromatography (HPLC). Transgenic plants were also compared with a control using a real-time quantification technique (to quantify the pathogen population), and transgenic and control plants were challenged with the local most virulent M. oryzae pathotype, P7.2. Based on the results, the Pikh gene encodes a hydrophilic protein with 18 sheets, 4 helixes, and 21 coils. This protein contains 401 amino acids, among which the amino acid sequence from 1 to 376 is a non-cytoplasmic region, that from 377 to 397 is a transmembrane region, and that from 398 to 401 is a cytoplasmic region with no identified disordered regions. The Pikh gene was up-regulated in the transgenic plants compared with the control plants. The quantity of the amino acid leucine in the transgenic rice plants increased significantly from 17.131 in the wild-type to 47.865 mg g(-1) in transgenic plants. The M. oryzae population was constant at 31, 48, and 72 h after inoculation in transgenic plants, while it was increased in the inoculated control plants. This study successfully clarified that over-expression of the Pikh gene in transgenic plants can improve their blast resistance against the M. oryzae pathotype P7.2.