The role of fumarase in the C4 grass Setaria viridis

• Grant number: 20/12362-8
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: October 01, 2020
• End date: July 31, 2024
• Field of knowledge: Agronomical Sciences - Agronomy
• Principal Investigator: Danilo da Cruz Centeno
• Grantee: Victória Alves Moreira
• Host Institution: Centro de Ciências Naturais e Humanas (CCNH). Universidade Federal do ABC (UFABC). Ministério da Educação (Brasil). Santo André , SP, Brazil
• Associated research grant: 18/15576-9 - Carbon metabolism in plants under different perspectives: searching alternatives for crop yield enhancement, AP.JP2
• Associated scholarship(s): 22/13884-3 - The role of fumarase in the C4 grass Setaria viridis, BE.EP.DD

Abstract

Cell respiration in plants has been studied in the late years, especially in those plants expressing the C3 photosynthetic metabolism. Despite the efforts on this topic, many questions remain unclear. This is even more evident when considering the interaction of cell respiration and other metabolic pathways in C4 photosynthetic metabolism. Some studies suggest that the metabolic control of the TCA cycle is mainly due to fumarase, malate dehydrogenase (MDH) and 2-oxoglutarate dehydrogenase, indicating that these enzymes could be sensible targets to the regulation of carbon flux to other pathways. Fumarase is responsible for the conversion of fumaric acid into malic acid. Transgenic plants of tomato with decreased activity of fumarase presented higher levels of fumaric acid and lower concentration of starch and sugar on leaves, associated to decreased photosynthetic rates due to stomatal closure. On the other hand, the same construct under the control of a fruit specific promoter lead to increased levels of transient starch in green fruit and sugars in mature fruits, as a result of diminished malic acid levels. Malic acid is considered one of the key metabolites in plants due to its known multiple functions, such as pH regulation, substrate for respiration or decarboxylation on C4 cycle. This indicates that malic acid acts as a potent metabolic regulator and alteration on its mitochondrial levels can result in changes on growth rate. However, the mechanisms are still not fully clear. Preliminary results on our lab (Young Researcher Project - part 1) points out that the downregulation of fumarase in Setaria viridis seem to have a huge impact on plant growth rates (not yet published). Moreover, transgenic plants are normally weak and produce a very small amount of seeds, with low percentage of viability. Intriguingly, photosynthetic rates are not changed, when considering CO2 assimilation per leaf area. Our hypothesis is that mitochondrial malic acid production is much more important for C4 than C3 plants, but the reason behind this impact remains unclear. (AU)