Search

Summary: Leucine‐rich repeat‐receptor‐like kinase (LRR‐RLK) is a large subfamily of plant RLKs; however, its role in cold tolerance is still unknown. A novel cold tolerance LRR‐RLK gene (MtCTLK1) in Medicago truncatula was identified using the transgenic lines overexpressing MtCTLK1 (MtCTLK1‐OE) and mtctlk1 lines with Tnt1 retrotransposon insertion. Compared with the wild‐type, MtCTLK1‐OE lines had increased cold tolerance and mtctlk1 showed decreased cold tolerance. The impaired cold tolerance in mtctlk1 could be complemented by the transgenic expression of MtCTLK1 or its homolog MfCTLK1 from Medicago falcata. Antioxidant enzyme activities and proline accumulation as well as transcript levels of the associated genes were increased in response to cold, with higher levels in MtCTLK1‐OE or lower levels in mtctlk1 lines as compared with wild type. C‐Repeat‐Binding Factors (CBFs) and CBF‐dependent cold‐responsive genes were also induced in response to cold, and higher transcript levels of CBFs and CBF‐dependent cold‐responsive genes were observed in MtCTLK1‐OE lines whereas lower levels in mtctlk1 mutants. The results validate the role of MtCTLK1 or MfCTLK1 in the regulation of cold tolerance through the CBF pathway, antioxidant defense system and proline accumulation. It also provides a valuable gene for the molecular breeding program to improve cold tolerance in crops. Significance Statement: A novel cold tolerance leucine‐rich repeat‐receptor‐like kinase was identified from Medicago truncatula. It confers cold tolerance through regulation on the C‐repeat‐binding factor cold response pathway, antioxidant defense, and proline accumulation. [ABSTRACT FROM AUTHOR]

Auxin induced in root culture (AIR12) is a single gene in Arabidopsis and codes for a mono‐heme cytochrome b, but it is unknown whether plant AIR12 is involved in abiotic stress responses. MfAIR12 was identified from Medicago falcata that is legume germplasm with great cold tolerance. Transcript levels of MfAIR12 and its homolog MtAIR12 from Medicago truncatula was induced under low temperature. Overexpression of MfAIR12 led to the accumulation of H2O2 in apoplast and enhanced cold tolerance, which was blocked by H2O2 scavengers, indicating that the increased cold tolerance was dependent upon the accumulated H2O2. In addition, declined cold tolerance was observed in Arabidopsis mutant air12, which could be restored by expressing MfAIR12. Compared to the wild type, higher levels of ascorbic acid and ascorbate redox state, as well as transcripts of the C repeat/dehydration responsive element‐binding factor (CBF) transcription factors and their downstream cold‐responsive genes, were observed in MfAIR12 transgenic lines, but lower levels of those in air12 mutant. It is suggested AIR12 confers cold tolerance as a result of the altered H2O2 in the apoplast that is signaling in the regulation of CBF cold response pathway and ascorbate homeostasis. AIR12 confers cold tolerance as a result of the altered H2O2 in apoplast that is signaling in the regulation of CBF pathway and its downstream cold‐responsive genes as well as ascorbic acid synthesis and redox state. [ABSTRACT FROM AUTHOR]