Redundancy or specificity of function? Multilple isoforms for plant malate.”

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

Tucumán, Argentina.

Congreso; • XLV CONGRESO DE LA SOCIEDAD ARGENTINA DE BIOQUÍMICA Y BIOLOGÍA MOLECULAR (SAIB); 2009

Sociedad Argentina de Bioquímica y Biología Molecular.

Malate is an important plant metabolite proposed to exhibit multiplicity of functions,both in C3 and C4 species. Malic enzyme (ME) is implicated in its oxidativedecarboxylation, generating CO2, NAD(P)H and pyruvate. However, it is surprising theexpression, even in the same sub-cellular compartment, of several MEs in both types ofplants. Thus, the open question is if these MEs are redundant or if they display anspecific role in plant metabolism. For example, Arabidopsis thaliana contains six genesencoding active ME. But, are all of them just involved in L-malate degradation? Theresults obtained, after characterizing the recombinant MEs and knock-out mutants,indicate that each isoenzyme displays an specific role in vivo, due to its expressionpattern and distinct biochemical properties. Moreover, the expression of a C4-ME inArabidopsis, revealed the importance of malate as respiratory substrate in this C3species. 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 sheathchloroplast, which display specific expression pattern with different biochemicalproperties. As a whole, the divergent properties of the ME isoenzymes suggest that eachone fulfils an exclusive metabolic function in vivo and that ME co-expression does notimply redundancy but represents specificity of function.