Redundancy or specificity of function? Multiple isoforms for plant malate oxidative decarboxylation

DRINCOVICH, M. F.; MAURINO, V. G.; GERRARD WHEELER, M. C.; TRONCONI, M. A.; SAIGO, M.; ALVAREZ, C. E.; ANDREO, C. S.

San Miguel de Tucumán

Congreso; XLV Reunión Anual SAIB; 2009

SAIB

Malate as an important plant metabolite proposed to exhibit multiplicity of functions, both in C3 and C4 species. Malic enzyme (ME) is implicated in its oxidative decarboxylation, generating CO2, NAD(P)H and pyruvate. However, it is surprising the expression, even in the same sub-cellular compartment, of several MEs in both types of plants. Thus, the open question is if these MEs are redundant or if they display an specific role in plant metabolism. For example, Arabidopsis thaliana contains six genes encoding active ME. But, are all of them just involved in L-malate degradation? The results obtained, after characterizing the recombinant MEs and knock-out mutants, indicate that each isoenzyme displays an specific role in vivo, due to its expression pattern and distinct biochemical properties. Moreover, the expression of a C4-ME in Arabidopsis, revealed the importance of malate as respiratory substrate in this C3 species. On the other hand, in the C4 species Zea mays, several MEs are also expressed, apart from the photosynthetic NADP-ME exclusively found in bundle sheath chloroplast, which display specific expression pattern with different biochemical properties. As a whole, the divergent properties of the ME isoensymes suggest that each one fulfils an exclusive metabolic function in vivo ant the ME co-expression does not imply redundancy but represents specificity of function.