Biosynthesis of isoprenoids via mevalonate is essential for cold acclimation in alfalfa

AYUB ND; SOTO GC; STRITZLER M; PAGANO ME; ARDILA FJ; RIOS RD

Capital Federal

Simposio; The 6th International symposium on the molecular breeding of forage and turf; 2010

INTA

The majority (>80%) of the Earth’s biosphere is cold and exposed to temperatures below 5°C throughout the year. It has been reported that organisms living at low temperature are exposed to oxidative stress generated by cold conditions. The isoprenoids are reduced and extremely diverse group of organic compounds that increase fitness in changing environments. The first step of isoprenoid biosynthesis via mevalonate is catalyzed by a tiolase II (EC 2.3.19) which condenses two molecules of acetyl-CoA to give acetoacetyl-CoA. Free CoASH is released at three points in isoprenoid biosynthesis, namely during the production of mevalonate from acetyl-CoA. We have identified and cloned a thiolase II from alfalfa (MsAACT1, GQ890698). Thiolase activity was experimentally demonstrated by using bacteria as heterologous expression system. Real-time RT-PCR analyses indicated that MsAACT1 transcripts are highly induced in roots and leaves under cold stress. In addition to transcriptional control, the condensation reaction by MsAACT1 was inhibited by CoASH. Taken together, these results indicate that this enzyme play a key role in the isoprenoid biosynthesis and is involved in low temperature adaptation. In order to evaluate this hypotesis, specific inhibitor of mevalonate pathway (mevastatine) was used to perturb biosynthetic flux in alfalfa seedlings and mature plants. Treatment of alfalfa with mevastatine resulted in decrease in chlorophyll levels and survival under cold stress. Addition of reduced compound ascorbic acid suppressed the cold sensitive phenotype of alfalfa challenged with mevastatine, suggesting a critical role of isoprenoids for maintenance of redox state in alfalfa during low temperature adaptation. Thus MsAACT1 can be used to increase isoprenoid content of plants and also to enhance tolerance to cold stress.