Sucrose transporters (SUCs or SUTs) play a central role, as they orchestrate sucrose allocation both intracellularly and at the whole plant level. Previously, we found AtSUC4 mutants changing sucrose distribution under drought and salt stresses. Here, we systematically examined the role of Arabidopsis AtSUC2 and AtSUC4 in response to abiotic stress. The results showed significant induction of AtSUC2 and AtSUC4 in salt, osmotic, low temperature and exogenous abscisic acid (ABA) treatments by public microarray data and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analyses. The loss-of-function mutation of AtSUC2 and AtSUC4 led to hypersensitive responses to abiotic stress and ABA treatment in seed germination and seedling growth. These mutants also showed higher sucrose content in shoots and lower sucrose content in roots, as compared with that in wild-type plants, and inhibited the ABA-induced expression of many stress- and ABA-responsive genes, especially ABFs and ABF-downstream and upstream genes. The loss-of-function mutant of AtSUC3, a unique putative sucrose sensor, reduced the expression of AtSUC2 and AtSUC4 in response to abiotic stresses and ABA. These findings confirmed that AtSUC2 and AtSUC4 are important regulators in plant abiotic stress tolerance that use an ABA signaling pathway, which may be crossed with sucrose signaling.

A newly isolated strain B69 with broad antimicrobial activity was identified as Paenibacillus elgii by 16S rRNA gene sequence analysis, along with physiological and biochemical characterization. Two antimicrobial compounds, named as Pelgipeptins A and B, were isolated from the culture medium using MCI GEL CHP20P column chromatography and HPLC methods. The molecular masses of Pelgipeptins A and B were 1072 and 1100 Da, respectively. The ESI-CID-MS and amino acid analysis suggested that both of them belonged to the polypeptin family, and Pelgipeptin A was unequivocally characterized as a new antibiotic. These two antibiotics were active against all the tested bacterial strains and displayed strong antifungal activity against several soil-borne fungal pathogens, with minimal inhibitory concentration values of 6.25-50 mug mL(-1). Furthermore, stability analysis indicated that the inhibitory activity of Pelgipeptins in the cell-free supernatant was unaffected during exposure to 60 degrees C for 2 h or a pH ranging from 1.0 to 8.0. Based on the strong antifungal activity and attractive biochemical properties, Pelgipeptins might provide an alternative resource of chemical pesticides for the biocontrol of plant diseases.

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Two lipopeptide antibiotics, pelgipeptins C and D, were isolated from Paenibacillus elgii B69 strain. The molecular masses of the two compounds were both determined to be 1,086 Da. Mass-spectrometry, amino acid analysis and NMR spectroscopy indicated that pelgipeptin C was the same compound as BMY-28160, while pelgipeptin D was identified as a new antibiotic of the polypeptin family. These two peptides were active against all the tested microorganisms, including antibiotic-resistant pathogenic bacterial strains such as methicillin-resistant Staphylococcus aureus (MRSA). Time-kill assays demonstrated that pelgipeptin D exhibited rapid and effective bactericidal action against MRSA at 4×MIC. Based on acute toxicity test, the intraperitoneal LD50 value of pelgipeptin D was slightly higher than that of the structurally related antimicrobial agent polymyxin B. Pelgipeptins are highly potent antibacterial and antifungal agents, particularly against MRSA, and warrant further investigation as possible therapeutic agents for bacteria infections resistant to currently available antibiotics.