Title : Plant i-AAA protease controls the turnover of the essential mitochondrial protein import component
Abstract:
Mitochondria are life-essential, multifunctional organelles that are the main sites of ATP production in cell. The bulk of mitochondrial proteins are involved in diverse metabolic pathways, such as the biosynthesis of cofactors like iron-sulphur clusters, and the metabolism of sugars, amino acids, and lipids. Due to the essential functions of these organelles, mitochondrial content, quality, and dynamics are tightly controlled. Mitochondrial integrity depends on balancing levels of different subunits of protein complexes. Selective removal of excess subunits by ATP – dependent proteolysis is one of the mechanisms employed by mitochondria in order to maintain protein homeostasis. This study focuses on a molecular function of plant mitochondrial inner membrane-embedded i – AAA protease, FTSH4. Lack of FTSH4 causes severe morphological and developmental abnormalities in plants grown under stress conditions. This is accompanied by decreased levels and activities of specific respiratory complexes, anomalies in mitochondrial morphology, and increased oxidative stress. However, the molecular mechanism that directly links the observed phenotypes of ftsh4 plants with the FTSH4 protease is still missing. We found that FTSH4 protease controls levels of the essential protein import component, Tim17-2, at the mitochondria. Tim17-2 is a core component of TIM23 translocase through which majority of mitochondrial preproteins are transported into the organelle. Plants that are lacking functional FTSH4 protease are characterized by significantly enhanced capacity of preprotein import through the TIM23 - dependent pathway. Together with the observation that FTSH4 prevents accumulation of Tim17-2, our data point towards a role of this i - AAA protease in the regulation of mitochondrial preprotein transport in plants. This work is supported by grant FUGA 2015/16/S/NZ3/00364 from National Science Centre awarded to Magdalena Opali?ska. Conference costs were supported by Wroclaw Centre of Biotechnology program “The Leading National Research Centre (KNOW) for years 2014-2018.Agronomically there are several differences between the hybrid and OP cultivars. We report differences in, yield plant density required to achieve maximum site yield, plant growth rates as measured by NDVI and destructive sampling and rates of field emergence. There are also farming systems aspects to be considered. For example adoption of the glyphosate resistant hybrids has been geographically specific with this technology used in ~60% of fields the northern cropping region. This is in response to difficulty controlling weeds that are resistant to other herbicide groups.
Economically cost of seed and technology fees for hybrids is around $30.00AUD/kg, whereas farmers can retain farm produced OP seed to sow the next crop for a tenth of this cost. Additionally there is a discount of approximately $40AUD per tonne for genetically modified canola against non-GM. The relative profitability of hybrid and OP depended on the yield potential of the site. When yield was lower than 1.2 t/ha it was more profitable to use an OP variety whereas in higher productivity situations/regions the improved yield of the hybrid compensated for additional seed cost and discounted sale price.
At an industry level there is strong support for farmers to have access to both OP and Hybrid varieties. This enables farmers to choose a low input risk minimisation strategy using OP seed or a higher risk profit maximisation strategy using hybrids in more productive regions. Security of seed supply is also an issue, as highlighted in 2017, when poor production of hybrid seed meant only 60% of the hybrid seed ordered could be supplied and OP seed was required to cover this shortage.
In summary there is a good case for the use of both hybrid and open pollinated plant types within the Western Australian environment and it is critical that farmers continue to have access to well adapted cultivars of both.
