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.

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In contrast to the extensive understanding of seed mucilage biosynthesis, much less is known about how mucilage is biodegraded and what role it plays in the soil where seeds germinate. We studied seed mucilage biodegradation by a natural microbial community. High-performance anionexchange chromatography (HPAEC) was used to determine monosaccharide composition in achene mucilage of Artemisia sphaerocephala. Mucilage degradation by the soil microbial community from natural habitats was examined by monosaccharide utilization tests using Biolog plates, chemical assays and phospholipid fatty acid (PLFA) analysis. Glucose (29.4%), mannose (20.3%) and arabinose (19.5%) were found to be the main components of achene mucilage. The mucilage was biodegraded to CO2 and soluble sugars, and an increase in soil microbial biomass was observed during biodegradation. Fluorescence microscopy showed the presence of mucilage (or its derivatives) in seedling tissues after growth with fluorescein isothiocyanate (FITC)-labelled mucilage. The biodegradation also promoted early seedling growth in barren sand dunes, which was associated with a large soil microbial community that supplies substances promoting seedling establishment. We conclude that biodegradation of seed mucilage can play an ecologically important role in the life cycles of plants especially in harsh desert environments to which A. sphaerocephala is well-adapted.

BackgroundCalcium-binding proteins that contain EF-hand motifs have been reported to play important roles in transduction of signals associated with biotic and abiotic stresses. To functionally characterize gens of EF-hand family in response to abiotic stress, an MtCaMP1 gene belonging to EF-hand family from legume model plant Medicago truncatula was isolated and its function in response to drought and salt stress was investigated by expressing MtCaMP1 in Arabidopsis.Methodology/Principal FindingsTransgenic Arabidopsis seedlings expressing MtCaMP1exhibited higher survival rate than wild-type seedlings under drought and salt stress, suggesting that expression of MtCaMP1 confers tolerance of Arabidopsis to drought and salt stress. The transgenic plants accumulated greater amounts of Pro due to up-regulation of P5CS1 and down-regulation of ProDH than wild-type plants under drought stress. There was a less accumulation of Na+ in the transgenic plants than in WT plants due to reduced up-regulation of AtHKT1 and enhanced regulation of AtNHX1 in the transgenic plants compared to WT plants under salt stress. There was a reduced accumulation of H2O2 and malondialdehyde in the transgenic plants than in WT plants under both drought and salt stress.Conclusions/SignificanceThe expression of MtCaMP1 in Arabidopsis enhanced tolerance of the transgenic plants to drought and salt stress by effective osmo-regulation due to greater accumulation of Pro and by minimizing toxic Na+ accumulation, respectively. The enhanced accumulation of Pro and reduced accumulation of Na+ under drought and salt stress would protect plants from water default and Na+ toxicity, and alleviate the associated oxidative stress. These findings demonstrate that MtCaMP1 encodes a stress-responsive EF-hand protein that plays a regulatory role in response of plants to drought and salt stress.

Tumour cell–derived heat shock proteins (HSPs) are used as vaccines for immunotherapy of cancer patients. However, it is proposed that the peptide chaperoned on HSPs, not HSPs themselves, elicited a potent immune response. Given that HSPs are highly expressed by most myeloma cells and vital to myeloma cell survival, we reasoned that HSPs themselves might be an ideal myeloma antigen. In the present study, we explored the feasibility of targeting HSPs themselves for treating multiple myeloma. We identified and chose HLA-A*0201-binding peptides from human HSPB1 (HSP27) and HSP90AA1 (HSP90), and confirmed their immunogenicity in HLA-A*0201 transgenic mice. Dendritic cells pulsed with HSPB1 and HSP90AA1 peptides were used to stimulate peripheral blood mononuclear cells from healthy volunteers and myeloma patients to generate HSP peptide-specific cytotoxic T lymphocytes (CTLs). HSP peptide-specific CTLs efficiently lysed HLA-A*0201+ myeloma cells (established cell lines and primary plasma cells) but not HLA-A*0201− myeloma cells in vitro, indicating that myeloma cells naturally express HSP peptides in the context of major histocompatibility complex class I molecules. More importantly, HSP peptide-specific CTLs effectively reduced tumour burden in the xenograft mouse model of myeloma. Our study clearly demonstrated that HSPs might be novel tumour antigens for immunotherapy of myeloma.