Molecular cloning and characterization of a gene encoding the proline transporter protein in common bean (Phaseolus vulgaris L.)

As a typical compatible solute, proline is accumulated in plants under environmental stresses. Proline transporter (ProT) plays an important role in proline distribution between plant organs. Using a candidate gene approach, we cloned a cDNA sequence for ProT from common bean (Phaseolus vulgaris L.) and designated the gene PvProT. The deduced amino acid sequence of PvProT showed high similarity to Bet/ProT proteins from other leguminous plants, and the highest similarity was observed with mothbean (Vigna aconitifolia L.) VuProT. Relative quantification of the mRNA level of PvProT using real-time PCR analysis showed that the PvProT transcript level was higher in leaves than in stems and roots of common bean plants subjected to drought and salt stress. Under 20% (w/w) PEG-6000 treatment, drought-resistant plants expressed a higher level of PvProT transcripts than drought-sensitive plants. Although heterologous expression of PvProT in the Escherichia coli mutant mkh13 showed that PvProT exhibited uptake activities for proline and betaine, no betaine content was detected in the common bean. These findings suggest that PvProT plays an important role in the transportation of proline in common bean plants exposed to drought and salt stress.