"Thioredoxins from bundle sheath and mesophyll cells: role in maize C4 enzyme reduction

OITAVÉN P.; ALVAREZ C.E.; ANDREO C.S.; DRINCOVICH M.F.

Rosario

Congreso; L CONGRESO DE LA SOCIEDAD ARGENTINA DE BIOQUÍMICA Y BIOLOGÍA MOLECULAR (SAIB); 2014

Thioredoxins are ubiquitous small proteins with a highly conserved active site which is linked to thiol redox exchange processes. In chloroplasts, thioredoxins make a connection between the light-mediated processes and the activity of many photosynthetic enzymes. Recent studies with corn chloroplasts show six different groups of thioredoxins with differential expression patterns in the two cell types: Vascular Bundle sheath (BSC) and Mesophyll Cells (MC). Furthermore, proteomic and transcriptomics studies indicate that most thioredoxins are expressed in the BSC cells, except for one belonging to the m4 group, which is localized in MC. Despite the important role of thioredoxins in the regulation of the photosynthetic process, they have not been characterized in maize yet. In the present work, two putative m4 type thioredoxins (called tioBSC and tioMC) were cloned and successfully expressed as recombinant proteins. TioBSC and tioMC show particular pattern of expression in BSC and MC from maize leaves. Moreover, both thioredoxins were able to catalyze, although to different extent, the reduction and activation of maize photosynthetic NADP-malic enzyme (ZmC4-NADP-ME), the enzyme responsible of the production of CO2 from malate in BSC chloroplasts. The structural basis for the better performance of tioBSC than tioMC in regulating ZmC4-NADP-ME activity are proposed