COMPARATIVE-ANALYSIS OF THE REGULATION OF EXPRESSION AND STRUCTURES OF 2 EVOLUTIONARILY DIVERGENT GENES FOR DELTA(1)-PYRROLINE-5-CARBOXYLATE SYNTHETASE FROM TOMATO

We isolated two tomato (Lycopersicon esculentum) cDNA clones, tomPRO1 and tomPRO2, specifying Delta(1)-pyrroline-5-carboxylate synthetase (P 5CS), the first enzyme of proline (Pro) biosynthesis. tomPRO1 is unusu al because it resembles prokaryotic polycistronic operons (M.G. Garcia -Rios, T. Fujita, P.C. LaRosa, R.D. Locy, J.M. Clithero, R.A. Bressan, L.N. Csonka [1997] Proc Natl Acad Sci USA 94: 8249-8254), whereas tom PRO2 encodes a full-length P5CS. We analyzed the accumulation of Pro a nd the tomPRO1 and tomPRO2 messages in response to NaCl stress and dev elopmental signals. Treatment with 200 mM NaCl resulted in a >60-fold increase in Pro levels in roots and leaves. However, there was a <3-fo ld increase in the accumulation of the tomPRO2 message and no detectab le induction in the level of the tomPRO1 message in response to NaCl s tress. Although pollen contained approximately 100-fold higher levels of Pro than other plant tissues, there was no detectable increase in t he level of either message in pollen. We conclude that transcriptional regulation of these genes for P5CS is probably not important for the osmotic or pollen-specific regulation of Pro synthesis in tomato. Usin g restriction fragment-length polymorphism mapping, we determined the locations of tomPRO1 and tomPRO2 loci in the tomato nuclear genome. Se quence comparison suggested that tomPRO1 is similar to prokaryotic P5C S loci, whereas tomPRO2 is closely related to other eukaryotic P5CS ge nes.