A novel Medicago truncatula calmodulin‐like protein (MtCML42) regulates cold tolerance and flowering time

Abstract

Calmodulin-like proteins (CMLs) are one of the Ca 2+ sensors in plants, but the functions of most CMLs remain unknown. The regulation of cold tolerance and flowering time by MtCML42 in Medicago truncatula and the underlying mechanisms were investigated using MtCML42-overexpressing plants and cml42 Medicago mutants with a Tnt1 retrotransposon insertion. Compared with the wild type (WT), MtCML42overexpressing lines had increased cold tolerance, whereas cml42 mutants showed decreased cold tolerance. The impaired cold tolerance in cml42 could b complemented by MtCML42 expression. The transcript levels of MtCBF1, MtCBF4, MtCOR413, MtCAS15, MtLTI6A, MtGolS1 and MtGolS2 and the concentrations of raffinose and sucrose were increased in response to cold treatment, whereas higher levels were observed in MtCML42-overexpressing lines and lower levels were observed in cml42 mutants. In addition, early flowering with upregulated MtFTa1 and downregulated MtABI5 transcripts was observed in MtCML42overexpressing lines, whereas delayed flowering with downregulated MtFTa1 and upregulated MtABI5 was observed in cml42. MtABI5 expression could complement the flowering phenotype in the Arabidopsis mutant abi5. Our results suggest that MtCML42 positively regulates MtCBF1 and MtCBF4 expression, which in turn upregulates the expression of some COR genes, MtGolS1 and MtGolS2, which leads to raffinose accumulation and increased cold tolerance. MtCML42 regulates flowering time through sequentially downregulating MtABI5 and upregulating MtFTa1 expression.

Optimizing raffinose family oligosaccharides content in plants: A tightrope walk

“…PhGolS1-1 was recognized as a direct target of PhZFP1 , a C2H2-type zinc finger protein, modulating galactinol synthesis and contributing to cold tolerance in Petunia hybrida ( Zhang et al., 2022 ). Increased cold tolerance as a result of raffinose accumulation has also been reported in maize ( Han et al., 2020 ), trifoliate orange ( Poncirus trifoliata L. ) ( Khan et al., 2021 ), and barrel clover ( Medicago truncatula ) ( Sun et al., 2021 ), where RS and GolS have been proposed to be the primary target of the associated transcription factors (HSFs, DREB1A/CBF3 and WRKY). Additionally, GolS1 was identified as a heat shock factor (HSF)-dependent gene of Arabidopsis involved in vegetative tissue-specific osmolyte synthesis during stress ( Panikulangara et al., 2004 ; Schramm et al., 2006 ; Nishizawa et al., 2008 ).…”

Calcium Mediated Cold Acclimation in Plants: Underlying Signaling and Molecular Mechanisms

“…Very recently, Solanum lycopersicum SlCML37 has been shown to interact with proteasome maturation factor SlUMP1 and has been reported in tomato fruit chilling stress tolerance ( Tang et al, 2021 ). Additionally, Medicago truncatula MtCML42 has been reported to regulate cold tolerance and flowering time ( Sun et al, 2021 ). Further, in rice, six new putative interacting partners of OsCML16 were identified (OsLRK5a, OsDCNL2, OsWD40-139, OsGDH1, OsCIP, and OsERD2).…”

Tolerant mechanism of model legume plant Medicago truncatula to drought, salt, and cold stresses

“…Besides, Qu et al (2016) indicates that the MfNAC3 plays roles in response to cold stress by regulating the expression of MtCBF4 . Recently, Sun et al (2021) identifies that MtCML42 positively regulates the expression of MtCBF1 and MtCBF4 , thereby upregulating the expression of the COR genes, MtGolS1 and MtGolS2 , and leads to raffinose accumulation and improved cold tolerance.…”