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

Abstract

Medicago falcata is a legume species that exhibits great capacity of tolerance to abiotic stresses. To elucidate the mechanism underlying tolerance of M. falcata to freezing, we compared the characteristics of M. falcata in response to cold acclimation and freezing with those of the legume model plant Medicago truncatula. M. falcata seedlings were more tolerant to freezing than M. truncatula, as evidenced by a lower value of EL(50) (temperature at which 50% electrolyte leakage after freezing) and greater survival rate for M. falcata than M. truncatula. Cold acclimation led to greater reduction in EL(50) for M. falcata than M. truncatula. Sucrose was the most abundant sugar in both M. falcta and M. truncatula, and a greater accumulation of sucrose and Pro in M. falcata than in M. truncatula during cold acclimation was observed. Cold acclimation induced small amounts of raffinose and stachyose in M. falcata, but not in M. truncatula. The activities of sucrose phosphate synthase and sucrose synthase were greater in M. falcata than in M. truncatula. In contrast, the activity of acid invertase was higher in M. truncatula than in M. falcata. There was an increase in transcript of CRT binding factor (CBF) upon exposure to low temperature in the two species. The low temperature-induced increase in transcript of CBF2 was much higher in M. truncatula than in M. falcata, while transcript of CBF3 in M. falcata was greater than that in M. truncatula. There were sustained increases in transcripts of cold acclimation specific (CAS), a downstream target of CBF, during cold acclimation and the increases were greater in M. falcata than in M. truncatula. These results demonstrate that accumulation of greater amounts of soluble sugars coupled with higher CBF3 and CAS transcript levels in M. falcata may play a role in conferring greater tolerance of M. falcata to freezing than that of M. truncatula.

Opposing control by transcription factors MYB61 and MYB3 Increases Freezing Tolerance by relieving C-repeat Binding Factor suppression

“…MtCAS15 (Medtr7g086340) is induced by low temperature in Medicago spp., and a positive correlation between freezing tolerance and its expression level was identified in Medicago spp. (Monroy et al, 1993a;Pennycooke et al, 2008;Zhang et al, 2011). In addition, MtLTI65 (AC235674_16) and MtY3G1 (Medtr2g014050; a late embryogenesis abundant protein) also were reported to participate in cold stress in previous studies (Nordin et al, 1993;Hincha and Thalhammer, 2012).…”

“…Pennycooke et al (2008) reported that Medicago truncatula does not cold acclimate. However, Zhang et al (2011) demonstrated that M. truncatula is able to increase its freezing tolerance after being subjected to cold-acclimating conditions. The different experimental conditions and methods used in these two studies may partly explain the different results (Pennycooke et al, 2008;Zhang et al, 2011).…”

“…However, Zhang et al (2011) demonstrated that M. truncatula is able to increase its freezing tolerance after being subjected to cold-acclimating conditions. The different experimental conditions and methods used in these two studies may partly explain the different results (Pennycooke et al, 2008;Zhang et al, 2011). By examining physiological markers of cold acclimation in M. truncatula, Thapa (2008) also independently demonstrated that this species undergoes cold acclimation.…”

“…In alfalfa (Medicago sativa), cold induces a calcium influx, which affects protein phosphorylation and the expression levels of cold acclimation-specific genes such as CAS15 and CAS18 (Mohapatra et al, 1989;Monroy et al, 1993aMonroy et al, , 1993bWolfraim et al, 1993;Monroy and Dhindsa, 1995). In M. truncatula and Medicago falcata, cold induces the expression of CBF1 to CBF3 and CAS genes (Pennycooke et al, 2008;Zhang et al, 2011). The expression level of MtCBF4 is induced by drought, salinity, and cold stress, and ectopic MtCBF4 expression in Arabidopsis enhances drought and salt tolerance, as well as salt tolerance when transiently expressed in M. truncatula roots (Li et al, 2011).…”

A Lipid-Anchored NAC Transcription Factor Is Translocated into the Nucleus and Activates Glyoxalase I Expression during Drought Stress

“…falcata, a model candidate for studying abiotic stressresponsive mechanisms in legumes, grows in adverse environments (Zhang et al, 2011). PI502449, a diploid variety of M. falcata, is more tolerant to drought and cold stresses than the model legume Medicago truncatula (Miao et al, 2015).…”