Plastidial NAD-dependent malate dehydrogenase is critical for embryo development and heterotrophic metabolism in Arabidopsis.
In illuminated chloroplasts, one mechanism involved in reduction-oxidation (redox) homeostasis is the malate-oxaloacetate (OAA) shuttle. Excess electrons from photosynthetic electron transport in the form of nicotinamide adenine dinucleotide phosphate, reduced are used by NADP-dependent malate dehydrogenase (MDH) to reduce OAA to malate, thus regenerating the electron acceptor NADP. NADP-MDH is a strictly redox-regulated, light-activated enzyme that is inactive in the dark. In the dark or in nonphotosynthetic tissues, the malate-OAA shuttle was proposed to be mediated by the constitutively active plastidial NAD-specific MDH isoform (pdNAD-MDH), but evidence is scarce. Here, we reveal the critical role of pdNAD-MDH in Arabidopsis (Arabidopsis thaliana) plants. A pdnad-mdh null mutation is embryo lethal. Plants with reduced pdNAD-MDH levels by means of artificial microRNA (miR-mdh-1) are viable, but dark metabolism is altered as reflected by increased nighttime malate, starch, and glutathione levels and a reduced respiration rate. In addition, miR-mdh-1 plants exhibit strong pleiotropic effects, including dwarfism, reductions in chlorophyll levels, photosynthetic rate, and daytime carbohydrate levels, and disordered chloroplast ultrastructure, particularly in developing leaves, compared with the wild type. pdNAD-MDH deficiency in miR-mdh-1 can be functionally complemented by expression of a microRNA-insensitive pdNAD-MDH but not NADP-MDH, confirming distinct roles for NAD- and NADP-linked redox homeostasis.
Institute of Agricultural Sciences, Eidgenössische Technische Hochschule Zürich, CH-8092 Zurich, Switzerland.
Seraina
S
Beeler
Hung-Chi
HC
Liu
Martha
M
Stadler
Tina
T
Schreier
Simona
S
Eicke
Wei-Ling
WL
Lue
Elisabeth
E
Truernit
Samuel C
SC
Zeeman
Jychian
J
Chen
Oliver
O
Kötting
D017360:Arabidopsis / Q000196:embryology* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D052818:Autotrophic Processes / Q000235:genetics; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D002940:Circadian Rhythm / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant / Q000235:genetics; D052836:Heterotrophic Processes / Q000235:genetics; D006720:Homozygote; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D055442:Metabolome / Q000235:genetics; D009024:Morphogenesis / Q000235:genetics; D016254:Mutagenesis, Insertional / Q000235:genetics; D010788:Photosynthesis; D021381:Protein Transport; D012639:Seeds / Q000196:embryology* / Q000201:enzymology*
D029681:Arabidopsis Proteins; D004251:DNA Transposable Elements; D002734:Chlorophyll; D008291:Malate Dehydrogenase