Bacillus subtilis: A plant-growth promoting rhizobacterium that also impacts biotic stress

Plants encounter many biotic agents, such as viruses, bacteria, nematodes, weeds, and arachnids. These entities induce biotic stress in their hosts by disrupting normal metabolism, and as a result, limit plant growth and/or are the cause of plant mortality. Some biotic agents, however, interact symbiotically or synergistically with their host plants. Some microbes can be beneficial to plants and perform the same role as chemical fertilizers and pesticides, acting as a biofertilizer and/or biopesticide. Plant growth promoting rhizobacteria (PGPR) can significantly enhance plant growth and represent a mutually helpful plant-microbe interaction. Bacillus species are a major type of rhizobacteria that can form spores that can survive in the soil for long period of time under harsh environmental conditions. Plant growth is enhanced by PGPR through the induction of systemic resistance, antibiosis, and competitive omission. Thus, the application of microbes can be used to induce systemic resistance in plants against biotic agents and enhance environmental stress tolerance. Bacillus subtilis exhibits both a direct and indirect biocontrol mechanism to suppress disease caused by pathogens. The direct mechanism includes the synthesis of many secondary metabolites, hormones, cell-wall-degrading enzymes, and antioxidants that assist the plant in its defense against pathogen attack. The indirect mechanism includes the stimulation of plant growth and the induction of acquired systemic resistance. Bacillus subtilis can also solubilize soil P, enhance nitrogen fixation, and produce siderophores that promote its growth and suppresses the growth of pathogens. Bacillus subtilis enhances stress tolerance in their plant hosts by inducing the expression of stress-response genes, phytohormones, and stress-related metabolites. The present review discusses the activity of B. subtilis in the rhizosphere, its role as a root colonizer, its biocontrol potential, the associated mechanisms of biocontrol and the ability of B. subtilis to increase crop productivity under conditions of biotic and abiotic stress.     

Isolation and characterization of three TaYUC10genes from wheat

YUCCA protein participates in a key rate-limiting step in the tryptophan-dependent pathway for auxin biosynthesis and is involved in numerous processes during plant development. In this study, the genomic and cDNA sequences of three TaYUC10 homoeologous genes were isolated. These sequences showed a very high conservation in coding region and the exon/intron structure, whereas their intron lengths were different. The cDNA and polypeptide chains of the three TaYUC10 genes were highly similar. These genes were most homologous to BdYUC10. Location analysis showed that TaYUC10.1 was present in chromosome 5BL. TaYUC10.3 was expressed in all parts of the wheat, but was predominant in the reproductive organs of mature wheat, such as flowering spikelets or fertilized embryos. In the fertilized embryos 28 d post-anthesis, expression of TaYUC10.3 was clearly increased with the development of seeds. This indicates that TaYUC genes may play a vital role in seed development. TaYUC10.3 overexpressed in Arabidopsis had a typical phenotype, excessive auxin accumulation also seen in higher plants, and showed increased spacing of silique and downward curling of the blade margin. Sterility was observed in adult transgenic plants, becoming more severe in late development. The floral structures of sterile plants were not integrated. TaYUC10 may be required for numerous wheat growth processes, including flower and seed development.     

A facile means for the identification of indolic compounds from plant tissues

The bulk of indole‐3‐acetic acid (IAA) in plants is found in the form of conjugated molecules, yet past research on identifying these compounds has largely relied on methods that were both laborious and inefficient. Using recent advances in analytical instrumentation, we have developed a simple yet powerful liquid chromatography–mass spectrometry (LC–MS)‐based method for the facile characterization of the small IAA conjugate profile of plants. The method uses the well‐known quinolinium ion (m/z 130.0651) generated in MS processes as a signature with high mass accuracy that can be used to screen plant extracts for indolic compounds, including IAA conjugates. We reinvestigated Glycine max (soybean) for its indoles and found indole‐3‐acetyl‐trytophan (IA‐Trp) in addition to the already known indole‐3‐acetyl‐aspartic acid (IA‐Asp) and indole‐3‐acetyl‐glutamic acid (IA‐Glu) conjugates. Surprisingly, several organic acid conjugates of tryptophan were also discovered, many of which have not been reported in planta before. These compounds may have important physiological roles in tryptophan metabolism, which in turn can affect human nutrition. We also demonstrated the general applicability of this method by identifying indolic compounds in different plant tissues of diverse phylogenetic origins. It involves minimal sample preparation but can work in conjunction with sample enrichment techniques. This method enables quick screening of IAA conjugates in both previously characterized as well as uncharacterized species, and facilitates the identification of indolic compounds in general.     

Yucasin is a potent inhibitor of YUCCA,a key enzyme in auxin biosynthesis

Indole‐3–acetic acid (IAA), an auxin plant hormone, is biosynthesized from tryptophan. The indole‐3–pyruvic acid (IPyA) pathway, involving the tryptophan aminotransferase TAA1 and YUCCA (YUC) enzymes, was recently found to be a major IAA biosynthetic pathway in Arabidopsis. TAA1 catalyzes the conversion of tryptophan to IPyA, and YUC produces IAA from IPyA. Using a chemical biology approach with maize coleoptiles, we identified 5–(4–chlorophenyl)‐4H‐1,2,4–triazole‐3–thiol (yucasin) as a potent inhibitor of IAA biosynthesis in YUC‐expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1‐His suggested that yucasin strongly inhibited YUC1‐His activity against the substrate IPyA in a competitive manner. Phenotypic analysis of Arabidopsis YUC1 over‐expression lines (35S::YUC1) demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. In addition, 35S::YUC1 seedlings showed resistance to yucasin in terms of root growth. A loss‐of‐function mutant of TAA1, sav3–2, was hypersensitive to yucasin in terms of root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor l –kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin‐treated sav3–2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. The present study showed that yucasin is a potent inhibitor of YUC enzymes that offers an effective tool for analyzing the contribution of IAA biosynthesis via the IPyA pathway to plant development and physiological processes.     

甾类激素炔雌醇、炔诺酮和左炔诺孕酮对拟南芥根生长的影响

采用不同浓度的人工合成甾类激素炔雌醇、炔诺酮和左炔诺孕酮处理拟南芥幼苗,研究3种激素对其根生长和根中内源激素含量的影响.结果表明:(1)30μg?L-1炔雌醇处理显著促进主根的伸长、侧根数及侧根总长的增加,促进主根根毛数和地下部鲜重的增加,增大内源IAA和iPAs含量,以及IAA/iPAs比值;3 000μg?L-1炔雌醇处理则增加主根的弯曲度;(2)炔诺酮活性相对较弱,浓度为300μg?L-1时对主根长、侧根数、侧根总长的促进效果最大,IAA含量增加而iPAs含量降低,IAA/iPAs比值最大;3 000μg?L-1炔诺酮则引起主根弯曲,抑制根毛的生长,但促进侧根数和的地下部鲜重的增加;(3)左炔诺孕酮的活性较高,3μg?L-1时对拟南芥主根长、主根根毛数增加最为显著;300μg?L-1时对侧根数、根毛密度的增幅最大,IAA含量增加,IAA/iPAs比值最大;3 000μg?L-1时显著抑制主根的生长和侧根的生成.     

Stimulation of indoleacetic acid production in a <Emphasis Type="Italic">Rhizobium</Emphasis> isolate of <Emphasis Type="Italic">Vigna mungo</Emphasis> by root nodule phenolic acids

The influence of endogenous root nodules phenolic acids on indoleacetic acid (IAA) production by its symbiont (Rhizobium) was examined. The root nodules contain higher amount of IAA and phenolic acids than non-nodulated roots. Presence of IAA metabolizing enzymes, IAA oxidase, peroxidase, and polyphenol oxidase indicate the metabolism of IAA in the nodules and roots. Three most abundant endogenous root nodule phenolic acids (protocatechuic acid, 4-hydroxybenzaldehyde and p-coumaric acid) have been identified and their effects on IAA production by the symbiont have been studied in l-tryptophan supplemented yeast extract basal medium. Protocatechuic acid (1.5 μg ml⁻¹) showed maximum stimulation (2.15-fold over control) of IAA production in rhizobial culture. These results indicate that the phenolic acids present in the nodule might serve as a stimulator for IAA production by the symbiont (Rhizobium). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

Studies on substrate specificity and activity regulating factors of trehalose-6-phosphate synthase of Saccharomyces cerevisiae

Purified trehalose-6-phosphate synthase (TPS) of Saccharomyces cerevisiae was effective over a wide range of substrates, although differing with regard to their relative activity. Polyanions heparin and chondroitin sulfate were seen to stimulate TPS activity, particularly when a pyrimidine glucose nucleotide like UDPG was used, rather than a purine glucose nucleotide like GDPG. A high V_max and a low K_m value of UDPG show its greater affinity with TPS than GDPG or TDPG. Among the glucosyl acceptors TPS showed maximum activity with G-6-P which was followed by M-6-P and F-6-P. Effect of heparin was also extended to the purification of TPS activity, as it helped to retain both stability and activity of the final purified enzyme. Metal co-factors, specifically MnCl₂ and ZnCl₂ acted as stimulators, while enzyme inhibitors had very little effect on TPS activity. Metal chelators like CDTA, EGTA stimulated enzyme activity by chelation of metal inhibitors. Temperature and pH optima of the purified enzyme were determined to be 40 °C and pH 8.5 respectively. Enzyme activity was stable at 0–40 °C and at alkaline pH.     

生长素信号转导途径及参与的生物学功能研究进展

生长素参与植物生长和发育诸多过程,调控众多生理反应,在植物整个生命周期中自始至终发挥着调节作用.研究生长素的作用机制,对深入认识植物生长发育的生理过程有着重要的意义.综述了与生长素信号转导途径相关的3类主要蛋白组分:生长素/吲哚乙酸蛋白(auxin/indoleacetic acids proteins,Aux/IAAs)、生长素响应因子(auxin response factors,ARFs)和SCF(SKP1-CDC53/CUL1-F-box)复合体,及相关的SGT1(suppressor of the G2 allele of skp1)基因,并对生长素相关基因表达的模式及其生物学功能进行了总结.