Molecular Physiological Analysis of the Two Plastidic ATP/ADP Transporters from Arabidopsis

Abstract

Arabidopsis (Arabidopsis thaliana) possesses two isoforms of plastidic ATP/ADP transporters (AtNTT1 and AtNTT2) exhibiting similar biochemical properties. To analyze the function of both isoforms on the molecular level, we examined the expression pattern of both genes by northern-blot analysis and promoter-b-glucuronidase fusions. AtNTT1 represents a sugar-induced gene mainly expressed in stem and roots, whereas AtNTT2 is expressed in several Arabidopsis tissues with highest accumulation in developing roots and young cotyledons. Developing lipid-storing seeds hardly contained AtNTT1 or -2 transcripts. The absence of a functional AtNTT1 gene affected plant development only slightly, whereas AtNTT2::T-DNA, AtNTT1-2::T-DNA, and RNA interference (RNAi) plants showed retarded plant development, mainly characterized by a reduced ability to generate primary roots and a delayed chlorophyll accumulation in seedlings. Electron microscopic examination of chloroplast substructure also revealed an impaired formation of thylakoids in RNAi seedlings. Moreover, RNAi-and AtNTT1-2::T-DNA plants showed reduced accumulation of the nuclear-encoded protein CP24 during deetiolation. Under short-day conditions reduced plastidic ATP import capacity correlates with a substantially reduced plant growth rate. This effect is absent under long-day conditions, strikingly indicating that nocturnal ATP import into chloroplasts is important. Plastidic ATP/ADP transport activity exerts significant control on lipid synthesis in developing Arabidopsis seeds. In total we made the surprising observation that plastidic ATP/ADP transport activity is not required to pass through the complete plant life cycle. However, plastidic ATP/ADP-transporter activity is required for both an undisturbed development of young tissues and a controlled cellular metabolism in mature leaves.

The Arabidopsis Thylakoid ADP/ATP Carrier TAAC Has an Additional Role in Supplying Plastidic Phosphoadenosine 5′-Phosphosulfate to the Cytosol

“…However, because of missing sulfation reactions in thylakoids, a PAPS (or PAP) transport across the thylakoid membrane is certainly not of physiological relevance. On the other hand, the IEM of plastids contains well-characterized ADP/ATP transporters (NTTs), which are primarily involved in ATP supply to chloroplasts during darkness (Neuhaus et al, 1997;Reiser et al, 2004). It has been demonstrated that mutants defective in NTT function do not survive extended darkness followed by illumination (Reinhold et al, 2007).…”

The Import and Export Business in Plastids: Transport Processes across the Inner Envelope Membrane

“…Within the past decade, the physiological functions of the two ATP transporters (NTTs) in Arabidopsis have been characterized. Extensive analysis of NTT antisense, RNA interference, and knockout plants revealed distinctive physiological roles of the NTTs in different types of plastids (Reiser et al, 2004).…”

Uridine-Ribohydrolase Is a Key Regulator in the Uridine Degradation Pathway of Arabidopsis

“…Plant growth was performed at 228C and 120 mmol quanta m 22 s 21 in a 10-h-light/14-h-dark regimen. For growth experiments with 5-FU, 5-FD, and 5-FO, surface-sterilized seeds were sown on Murashige and Skoog plates as described earlier (Reiser et al, 2004). Growth of seedlings in hydroponic culture was performed as described by Scheible et al (2004).…”