Molecular Cloning and Characterization of a cDNA Encoding Proline Transporter in Rice

Abstract

A cDNA encoding a proline (Pro) transporter (ProT) was isolated and characterized from a cDNA library prepared from 14-d-old seedlings of Oryza sativa cv. Akibare. The deduced amino acid sequence of the rice ProT protein (OsProT) had 68.8% homology to the ProT protein 1 from Arabidopsis thaliana and 59.6% homology to that from Lycopersicon esculentum. Northern blot analysis revealed that the gene for OsProT (OsProT) was expressed in all organs examined, comparatively strongly in leaf sheath and stem. Salt treatment did not induce expression of OsProT but strongly induced expression of the gene for delta1-pyrroline-5-carboxylate synthetase (P5CS), a key enzyme in Pro biosynthesis. Southern blot analysis revealed that OsProT has a gene family. OsProT specifically transported L-Pro in a transport assay using Xenopus laevis oocytes.

The AtProT Family. Compatible Solute Transporters with Similar Substrate Specificity But Differential Expression Patterns

“…In tomato, expression of LeProT1 was shown to be confined to pollen and expression correlated with elevated Pro levels. In contrast, AtProT1 and the rice homolog OsProT did not show any regulation of expression under stress conditions (Rentsch et al, 1996;Igarashi et al, 2000).…”

“…In the last few years, genes encoding transporters for the compatible solutes Pro and Gly betaine were isolated from a number of plant species, including Arabidopsis (AtProT1 and AtProT2; Rentsch et al, 1996), tomato (Lycopersicon esculentum; LeProT1-3; Schwacke et al, 1999), rice (Oryza sativa; OsProT; Igarashi et al, 2000), barley (Hordeum vulgare; HvProT; Ueda et al, 2001), orach (Atriplex hortensis; AhProT1; accession no. AAF76897), and mangrove (Avicennia marina; AmT1-3; Waditee et al, 2002).…”

Proline metabolism and transport in plant development

“…Consistent with the latter result, the affinity of the AtProTs for GABA was much lower than for proline or glycine betaine (4.5 mM compared to 0.5 and 0.2 mM, respectively Grallath et al 2005). While the selectivity of rice ProT has not been investigated in detail, barley HvProT recognized only L-proline efficiently, though with a higher affinity than any of the other ProTs (Igarashi et al 2000;Ueda et al 2001). These data on substrate selectivity of AAPs, LHTs and ProTs show that in plants both transporters with low and high selectivity for proline exist, indicating a role in general transfer of nitrogen and in proline-specific functions, respectively.…”

Transgenic rice expressing a cassava (Manihot esculenta Crantz) plasma membrane gene MePMP3-2 exhibits enhanced tolerance to salt and drought stresses

“…To obtain further insight into the molecular mechanisms accounting for the resistance of transgenic plants to salt (140 mM NaCl) and drought (20% PEG) stresses, we analyzed the expression of several relevant rice stress-related genes in the MePMP3-2 transgenic lines and in the WT, including OsProT (Igarashi et al, 2000) and OsP5CS (Igarashi et al, 1997), which are related to Pro accumulation, and OsDREB2A and OsLEA3 (Xiao et al, 2007), which are markers of ABA-dependent and ABA-independent signaling. There were no significant differences in the levels of OsProT, OsP5CS, OsDREB2A, and OsLEA3 expression between the MePMP3-2 transgenic lines and the WT plants under normal growth conditions (Figure 7A-D).…”

“…In order to survive under these environmental stress conditions, plants have evolved sophisticated mechanisms of adaptation including the regulating of multiple genes involved in stress-tolerance (Sahi et al, 2006). Genes related to stress-tolerance in rice include OsP5CS encoding D 1 -pyrroline-5-carboxylate (P5C) synthetase, which is thought to control the accumulation of proline (Pro) under high salt conditions (Igarashi et al, 1997), the Pro transporter gene OsProT (Igarashi et al, 2000), the dehydration-responsive element-binding transcription factor gene OsDREB2A, which is induced by high temperature, drought, and high salinity stresses in an ABA-independent manner, and the late embryogenesis abundant protein gene OsLEA3, which encodes an osmoprotective hydrophilin and depends on ABA for activation by abiotic stresses (Xiao et al, 2007). The activation of these genes, which protect plants from oxidative damage caused by salt, drought, and oxidative stresses, is closely linked to the production of malondialdehyde (MDA) and Pro, and these are frequently used as markers of stress responses.…”