Study On The Role Of DFR1 Gene In Environmental Stress In Arabidopsis

As sessile organisms,plants frequently face unfavourable environmental stresses such as drought and freezing.Proline accumulation is one of the most important adaptation mechanisms in response to these stresses in many plant species.Although proline metabolism has been well documented,the molecular regulation mechanism of proline homeostasis in response to these stresses is largely unknown.Here,we identified a novel gene DFR1(Drought and Freezing Responsive gene 1)encoding an unkown mitochondria protein that is involved in regulation of proline degradation in Arabidopsis.Two alternatively spliced isoforms of DFR1(DFR1.1 and DFR1.2)were identified and their expressions were strongly induced by both drought and cold stresses.The DFR1 knockdown mutants showed hypersensitivity to drought and freezing stresses,whereas the transgenic plants over-expressing DFR1.1(DFR1.1OE)and DFR1.2(DFR1.2OE)exhibited enhanced tolerance.Moreover,DFR1 conferred stress tolerance without growth penalty under normal condition,but it pronounced plant biomass under long-term mild drought and cold stresses.Surprizingly,absolute absence of DFR1 is lethal,suggesting that DFR1 is vital for plant growth and development.Further study showed that DFR1-mediated drought and freezing tolerance was positively correlated with the proline accumulation level.Importantly,we found that both DFR1.1 and DFR1.2 were able to physically interact with PDH1,PDH2 and P5 CDH,three enzymes conferring proline degradation,and suppress their activities.Additionally,once the stress was removed,DFR1 level was quickly down-regulated and its inhibition on PDH and P5 CDH activities was alleviated to degrade excess proline.Genetic epistasis analysis showed that DFR1 acts upstream of PDH1/2 and P5 CDH to positively regulate proline accumulation as well as drought and freezing tolerance.Taken together,our results demonstrate a novel regulatory pathway that,in response to drought and freezing stresses,DFR1 interacts with PDH1/2 and P5 CDH to abrogate their activities to maintain proline homeostasis,thereby conferring drought and freezing tolerance.Proline is a precursor of many flavor compounds such as glycine betaine and 2-acetyl-1-pyrroline,which is very important for improvement in food quality,thus study on proline metabolism is also meaningful in area of food biotechnology.