Chloroplasts reloaded

Researchers from the University of Nebraska found that adding human genes to tobacco plants increases their resilience. For some time, scientists have been studying a phenomenon called program cell death (PCD), in which a cell is told to commit suicide. Extensive research about PCD has shown to be very beneficial for understanding cellular functions that directly influence human health. For instance, it is now known that faulty PCD is connected to important mammalian diseases such as cancer, AIDS and strokes. One way of finding out more about PCD is to study the differences in plants and humans. Both plants and animals have similar forms of PCD, yet they also differ in certain ways. A notable difference lies with a group of PCD regulators called the Bcl-2 family of proteins in mammals. The Bcl-2 family members are divided into two groups: those that activate PCD and those that prevent PCD. So far, a similar group of proteins that perform similar functions in plants has not been found. Dr. Martin B. Dickman and Dr. Shaorong Chen from the Department of Plant Pathology of the University in Nebraska showed that Bcl-2 family members (Bcl-2, Bcl-xL, CED-9) can gather in tobacco chloroplasts and inhibit plant PCD, as they do in mammalian mitochondria. They recently published their work in the Journal of Experimental Botany. For their experiments they generated transgenic tobacco plants with genes that produce proteins from the Bcl-2 family (Bcl-2, Bcl-xL, CED-9), which are known to prevent PCD in humans and worms. Upon closer analysis, the researchers noticed an interesting phenomenon – the proteins that prevented PCD ended up in the chloroplasts and mitochondria of the tobacco plants. This was an essential first step, because Bcl-2 proteins in mammals are located in the mitochondria, which is similar to a plant’s chloroplast. The next step for the researchers was to see if the proteins could perform the same function in chloroplasts. To test this, Dr. Dickman and Dr. Shaorong treated the transgenic tobacco varieties with three herbicides that effect the chloroplast, thus inducing death. To their surprise, the genetically enhanced tobacco varieties survived and did not show any sign of plant PCD, while control tobacco varieties (non-transgenic) underwent PCD. To make sure that the inserted proteins were responsible for the inhibition of plant PCD, Dr. Dickman’s laboratory generated a mutant tobacco variety (Bcl2ΔBH4) that contained deletions at key points. These mutations caused the three proteins (Bcl-2, Bcl-xL, CED-9) to no longer function properly, but they would still be produced within the tobacco varieties. The mutants, as with the control tobacco varieties, died after treatment with herbicides. In addition, the researchers wanted to ensure that the results were chloroplast-dependent. To prove that the inserted proteins effected the chloroplasts, they treated the enhanced tobacco varieties with same herbicides, however this time in the dark. Why? Chloroplasts work in two pathways. One, driven by light, which through a chain reaction produces chemical energy which a plant stores as energy. This part of photosynthesis occurs in a part of the chloroplast called the thykaloid. Then in the dark, plants convert the stored energy into sugar. Thus the researchers performed the same experiments in the dark. Their results showed that herbicides had no effect on the cells, because the herbicides only effect certain proteins that are active during the first stage of photosynthesis. As a result the research groups found that the Bcl-2 family members localize to tobacco membranes and inhibit herbicide-induced PCD. Thus Dr. Dickman and Dr. Shaorong provided strong evidence that chloroplast are involved in plant PCD. The ability to prevent plants from undergoing unnecessary PCD, should be quite beneficial for the future plant breeding. Dr. Dickman told Checkbiotech, “If these genes or functional equivalents can be utilized under field conditions; crop plants will have value added enhanced agronomic traits.” This is something every farmer is looking for – crops that are more resilient and dependable. Dr. Dickman’s and Dr. Shaorong’s results are a great step forward for plant physiology, yet it doesn’t stop there. Their could also lead to medical solutions for human health as well. Checkbiotech asked Dr. Dickman if any medical applications exist that might help researchers find new drugs against cancer. Dr. Dickman told Checkbiotech that plant genes may provide new and unique targets in the future. "Source":[ http://www.checkbiotech.org/root/index.cfm?fuseaction=news&doc_id=12094&start=11&control=179&page_start=1&page_nr=101&pg=1]

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