The mitochondrial NAD ⁺ transporter (NDT1) plays important roles in cellular NAD ⁺ homeostasis in Arabidopsis thaliana

Summary

Nicotinamide adenine dinucleotide ( NAD ⁺) is an essential coenzyme required for all living organisms. In eukaryotic cells, the final step of NAD ⁺ biosynthesis is exclusively cytosolic. Hence, NAD ⁺ must be imported into organelles to support their metabolic functions. Three NAD ⁺ transporters belonging to the mitochondrial carrier family ( MCF) have been biochemically characterized in plants. AtNDT1 ( At2g47490), focus of the current study, At NDT2 ( At1g25380), targeted to the inner mitochondrial membrane, and At PXN ( At2g39970), located in the peroxisomal membrane. Although At NDT1 was presumed to reside in the chloroplast membrane, subcellular localization experiments with green fluorescent protein ( GFP) fusions revealed that At NDT1 locates exclusively in the mitochondrial membrane in stably transformed Arabidopsis plants. To understand the biological function of At NDT1 in Arabidopsis, three transgenic lines containing an antisense construct of At NDT1 under the control of the 35S promoter alongside a T‐ DNA insertional line were evaluated. Plants with reduced At NDT1 expression displayed lower pollen viability, silique length, and higher rate of seed abortion. Furthermore, these plants also exhibited an increased leaf number and leaf area concomitant with higher photosynthetic rates and higher levels of sucrose and starch. Therefore, lower expression of At NDT1 was associated with enhanced vegetative growth but severe impairment of the reproductive stage. These results are discussed in the context of the mitochondrial localization of At NDT1 and its important role in the cellular NAD ⁺ homeostasis for both metabolic and developmental processes in plants.

Significance Statement

The mitochondrial NAD ⁺ carrier (NDT1) plays an important role in cellular NAD ⁺ homeostasis in leaves. Impaired NDT1 function results in reduced pollen grain viability, tube growth and seed filling, seed germination and seedling establishment.