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Wu Q.,Kansas State University | Wu Q.,Cold Spring Harbor Laboratory | Shigaki T.,Papua New Guinea National Agricultural Research Institute | Han J.-S.,Kyungpook National University | And 3 more authors.
Plant Molecular Biology | Year: 2012

Deregulated expression of an Arabidopsis H+/Ca2+ antiporter (sCAX1) in agricultural crops increases total calcium (Ca2+) but may result in yield losses due to Ca2+ deficiency-like symptoms. Here we demonstrate that co-expression of a maize calreticulin (CRT, a Ca2+ binding protein located at endoplasmic reticulum) in sCAX1-expressing tobacco and tomato plants mitigated these adverse effects while maintaining enhanced Ca2+ content. Co-expression of CRT and sCAX1 could alleviate the hypersensitivity to ion imbalance in tobacco plants. Furthermore, blossom-end rot (BER) in tomato may be linked to changes in CAX activity and enhanced CRT expression mitigated BER in sCAX1 expressing lines. These findings suggest that co-expressing Ca2+ transporters and binding proteins at different intracellular compartments can alter the content and distribution of Ca2+ within the plant matrix. © 2012 Springer Science+Business Media Dordrecht. Source

Manohar M.,Baylor College of Medicine | Manohar M.,Texas A&M University | Shigaki T.,Papua New Guinea National Agricultural Research Institute | Mei H.,Baylor College of Medicine | And 5 more authors.
Biochemistry | Year: 2011

Plant calcium (Ca 2+) gradients, millimolar levels in the vacuole and micromolar levels in the cytoplasm, are regulated in part by high-capacity vacuolar cation/H + exchangers (CAXs). Several CAX transporters, including CAX1, appear to contain an approximately 40-amino acid N-terminal regulatory region (NRR) that modulates transport through N-terminal autoinhibition. Deletion of the NRR from several CAXs (sCAX) enhances function in plant and yeast expression assays; however, to date, there are no functional assays for CAX3 (or sCAX3), which is 77% identical and 91% similar in sequence to CAX1. In this report, we create a series of truncations in the CAX3 NRR and demonstrate activation of CAX3 in both yeast and plants by truncating a large portion (up to 90 amino acids) of the NRR. Experiments with endomembrane- enriched vesicles isolated from yeast expressing activated CAX3 demonstrate that the gene encodes Ca 2+/H + exchange with properties distinct from those of CAX1. The phenotypes produced by activated CAX3-expressing in transgenic tobacco lines are also distinct from those produced by sCAX1-expressing plants. These studies demonstrate shared and unique aspects of CAX1 and CAX3 transport and regulation. © 2011 American Chemical Society. Source

Shigaki T.,Papua New Guinea National Agricultural Research Institute
Recent Patents on Food, Nutrition and Agriculture | Year: 2014

The Pacific countries are small in land mass and therefore represent one of the most fragile ecosystems. Due to the isolation of these island counties, these are home to unique species of plants and animals as well as crop varieties and landraces. Biosafety issues in the Pacific countries, therefore, require special attention to take these factors into account. The issues are shared with other small island nations such as the Caribbean countries. Although most Pacific countries do not have scientific capacity to develop genetically modified organisms (GMOs), they are inadvertently introduced from the developed world. As the countries do not have appropriate capacity to monitor the introduction and commerce of GMO's, it is imperative to establish biosafety legislation and capacity by pooling the resources within the Pacific countries. © 2014 Bentham Science Publishers. Source

Manohar M.,Baylor College of Medicine | Manohar M.,Texas A&M University | Shigaki T.,Papua New Guinea National Agricultural Research Institute | Hirschi K.D.,Baylor College of Medicine | Hirschi K.D.,Texas A&M University
Plant Biology | Year: 2011

Inorganic cations play decisive roles in many cellular and physiological processes and are essential components of plant nutrition. Therefore, the uptake of cations and their redistribution must be precisely controlled. Vacuolar antiporters are important elements in mediating the intracellular sequestration of these cations. These antiporters are energized by the proton gradient across the vacuolar membrane and allow the rapid transport of cations into the vacuole. CAXs (for CAtion eXchanger) are members of a multigene family and appear to predominately reside on vacuoles. Defining CAX regulation and substrate specificity have been aided by utilising yeast as an experimental tool. Studies in plants suggest CAXs regulate apoplastic Ca 2+ levels in order to optimise cell wall expansion, photosynthesis, transpiration and plant productivity. CAX studies provide the basis for making designer transporters that have been used to develop nutrient enhanced crops and plants for remediating toxic soils. © 2011 German Botanical Society and The Royal Botanical Society of the Netherlands. Source

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