VALERI, MARIA CRISTINA
Metabolic control of the anaerobic response in Arabidopsis
Scientific disciplinary sector
Corso di studi
SCIENZE AGRARIE E BIOTECNOLOGIE - Agrobiosciences
relatore Prof. PERATA, PIERDOMENICO
Data inizio appello
Plants metabolism is considered as a complex of events like photosynthesis, respiration, synthesis and degradation of organic compounds. Together, these reactions are involved in the growth and development of the plant. Through the glycolysis, glucose derived from sucrose cleavage or degradation of starch, is converted into pyruvate. Normally, in aerobic conditions, pyruvate is completely oxidized to carbon dioxide and water with the production of a large amount of high-energy compounds. In nature it may happen that the level of oxygen suddenly collapses, for example in the case of heavy precipitation that often leads to the flooding of the soil. Another important aspect is the lack of oxygen at the tissue level, which is shown with a gradient of oxygen that can affect normal metabolic activity of the plant itself. Plants have developed a fundamental mechanism for their survival, which allows the best utilization of carbon stocks in the form of starch and soluble sugars. The response of plants to adverse environmental conditions occurs through the induction of genes involved in carbon metabolism. In the metabolism of sugars starch degradation is a crucial process. The majority of plants store its carbohydrates in the form of starch or sucrose. Genes induced in low oxygen conditions include those encoding enzymes involved in carbohydrate metabolism and fermentation. These pathways are required in the growth and development of the plant and consequently they are involved in survival. Sugar availability is therefore of crucial importance for energy production under hypoxia. The aim of this research is therefore to understand the relationship between sugar metabolism and oxygen deficiency and more precisely, the importance of sugars in plant survival. We show that Arabidopsis plants require starch for surviving during submergence and providing the effective induction of anaerobic genes. The starch-less pgm mutant is highly sensitive to submergence and also it is less able to induce anaerobic genes, compared to the wild-type. Treating wild-type plants under low oxygen conditions, inducing sugar starvation, results in a weak induction of alcohol dehydrogenase (ADH) and other anaerobic genes. The induction of the anaerobic genes requires transcription factors belonging to the group VII Ethylene Responsive Factors (ERF-VII) that, together with Plant Cysteine Oxidases (PCOs) act as an oxygen sensing mechanism. Under low oxygen conditions, RAP2.12 and the other two constitutively expressed group VII ERFs, RAP2.2, RAP2.3, stable and redundantly activate the core anaerobic response in Arabidopsis. The RAP2.12 dependent activation of the downstream genes is essential for plant survival under submergence. We show that repression of this pathway by sugar starvation occurs downstream of the hypoxia-dependent stabilization of ERF-VII proteins and independently of the energy sensor protein kinases SnRK1 (SNF1-related kinase 1).
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