Cold acclimation-induced freezing tolerance of Medicago truncatula seedlings is negatively regulated by ethylene.

To evaluate the role of ethylene in cold acclimation and cold stress, freezing tolerance and characteristics associated with cold acclimation were investigated using legume model plant Medicago truncatula Gaertn Jemalong A17. There was a rapid suppression of ethylene production during cold acclimation in A17 plants. Ethylene level was negatively correlated with freezing tolerance as inhibition of ethylene biosynthesis by inhibitors of ethylene biosynthesis enhanced freezing tolerance, while exogenous application of ethylene reduced cold acclimation-induced freezing tolerance. The involvement of ethylene signaling in modulation of freezing tolerance and cold acclimation was further studied using ethylene-insensitive mutant sickle skl. Although skl mutant was more tolerant to freezing than its wild-type counterpart A17 plants, cold acclimation enhanced freezing tolerance in 17 plants, but not in skl mutant. Expression of several ethylene response genes including EIN3, EIN3/EIL and ERFs was suppressed in skl mutant compared to A17 plants under non-cold-acclimated conditions. Cold acclimation downregulated expression of EIN3, EIN3/EIL and ERFs in A17 plants, while expression patterns of these genes were relatively constant in skl mutant during cold acclimation. Cold acclimation-induced increases in transcription of MtCBFs and MtCAS15 were suppressed in skl mutant compared with A17 plants. These results suggest that MtSKL1 is required for perception of the change of ethylene level in M. truncatula plants for the full development of the cold acclimation response by suppressing expression of MtEIN3 and MtEIN3/EIL1, which in turn downregulates expression of MtERFs, leading to the enhanced tolerance of M. truncatula to freezing by upregulating MtCBFs and MtCAS15.

Zhao M ，Liu W ，Xia X ，Wang T ，Zhang WH ... -  《-》

Comparative studies on tolerance of Medicago truncatula and Medicago falcata to freezing.

Zhang LL ，Zhao MG ，Tian QY ，Zhang WH ... -  《-》

Elevated CO2 decreases the response of the ethylene signaling pathway in Medicago truncatula and increases the abundance of the pea aphid.

The performance of herbivorous insects is greatly affected by plant nutritional quality and resistance, which are likely to be altered by rising concentrations of atmospheric CO2 . We previously reported that elevated CO2 enhanced biological nitrogen (N) fixation of Medicago truncatula, which could result in an increased supply of amino acids to the pea aphid (Acyrthosiphon pisum). The current study examined the N nutritional quality and aphid resistance of sickle, an ethylene-insensitive mutant of M. truncatula with supernodulation, and its wild-type control A17 under elevated CO2 in open-top field chambers. Regardless of CO2 concentration, growth and amino acid content were greater and aphid resistance was lower in sickle than in A17. Elevated CO2 up-regulated N assimilation and transamination-related enzymes activities and increased phloem amino acids in both genotypes. Furthermore, elevated CO2 down-regulated expression of 1-amino-cyclopropane-carboxylic acid (ACC), sickle gene (SKL) and ethylene response transcription factors (ERF) genes in the ethylene signaling pathway of A17 when infested by aphids and decreased resistance against aphids in terms of lower activities of superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO). Our results suggest that elevated CO2 suppresses the ethylene signaling pathway in M. truncatula, which results in an increase in plant nutritional quality for aphids and a decrease in plant resistance against aphids.

Guo H ，Sun Y ，Li Y ，Liu X ，Zhang W ，Ge F ... -  《-》

Identification of ethylene-mediated protein changes during nodulation in Medicago truncatula using proteome analysis.

Prayitno J ，Imin N ，Rolfe BG ，Mathesius U ... -  《-》

Identification of tissue-specific and cold-responsive lncRNAs in Medicago truncatula by high-throughput RNA sequencing.

Zhao M ，Wang T ，Sun T ，Yu X ，Tian R ，Zhang WH ... -  《BMC PLANT BIOLOGY》