Effect of thermal stress on amino acid and gene expression profiles in two local flax varieties with contrasting cold tolerance

Environmental stresses such as cold and heat are adversely affecting all aspects of crop plants including yield. In this study, the contents of fourteen amino acids and expression levels of four transcription factor genes including MYB1-1, KRP2, ERF and WRKY40 were analyzed in TN-97-2 (cold sensitive) and TN-97-290 (cold tolerant) local flax varieties under cold and heat stresses conditions. Seeds of two local flax varieties were grown in growth chamber of Biotechnology Institute of Urmia University, Urmia, Iran, under control conditions for 30 days. Then, plants were subjected to three different thermal regimes including control (25± 1°C), cold (4 ± 1°C) and heat (37 ± 1 °C) for three consecutive days.  Cold stress significantly increased the Asp, His, Ala and Met amino acids contents in both varieties. TN-97-290 variety exhibited less decline in His, Val, Phe, Iso and Leu contents than TN- 97- 2 variety under heat stress. Cold stress increased expression of ERF and WRKY40 mRNAs while heat stress elevated transcript levels of KRP2 and MYB1-1 genes in TN-97-290 variety. In summary, Asp, Glu, His, Ala and Met amino acids could be exogenously applied to flax plants by either foliar spray or root supplement to tolerate cold stress conditions. In addition, application of Ser and Pro amino acids may aid conferring heat tolerance to cold sensitive flax plants. The positive response of ERF and WRKY40 genes (cold stress) and KRP2 and MYB1-1 (heat stress) in TN-97-290 variety suggests their over-expression assist protecting flax plants under cold and heat stresses.