A conserved mechanism for nitrile metabolism in bacteria and plants
A conserved mechanism for nitrile metabolism in bacteria and plants
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DOI：
10.1111/j.1365-313x.2008.03682.x
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发表时间：
2009-01-01
期刊：
影响因子：
7.2
通讯作者：
Preston, Gail M.
中科院分区：
文献类型：
--
作者：
Howden, Andrew J. M.;Jill Harrison, C.;Preston, Gail M.
荧光假单胞菌SBW25是一种促进植物生长的细菌，可以有效地定殖在一系列植物的叶表面和根际。以前的研究已经确定了在甜菜根际表达的荧光假单胞菌SBW25中可能存在的植物诱导硝化酶基因（pinA）。硝化酶在植物、细菌和真菌中都有特征，被认为在腈的解毒、氮的利用和植物激素的合成中起重要作用。我们发现pinA是一种nit4型腈酶，可以催化β -氰-l-丙氨酸的水解，而β -氰-l-丙氨酸是植物环境中常见的一种腈，也是植物氰化物解毒途径的中间体。在植物中，氰化物转化为β -氰-l-丙氨酸，随后被NIT4解毒为天冬氨酸和氨。在荧光假单胞菌SBW25中，pinA在β -氰-l-丙氨酸和β -氰-l-丙氨酸前体氰化物和半胱氨酸的存在下被诱导。pinA允许荧光假单胞菌SBW25使用β -氰-l-丙氨酸作为氮源，并耐受这种腈的有毒浓度。此外，pinA被证明可以补充拟南芥中的NIT4突变，使植物能够在β -氰-l-丙氨酸浓度下生长，否则会被证明是致命的。有趣的是，在野生型拟蓝中，pinA的过表达不仅导致了高浓度β -氰-l-丙氨酸的生长增加，而且在缺乏外源β -氰-l-丙氨酸的情况下，也导致了根的伸长增加，这表明β -氰-l-丙氨酸硝化酶活性对根生理和根发育有显著影响。
Pseudomonas fluorescens SBW25 is a plant growth-promoting bacterium that efficiently colonises the leaf surfaces and rhizosphere of a range of plants. Previous studies have identified a putative plant-induced nitrilase gene (pinA) in P. fluorescens SBW25 that is expressed in the rhizosphere of sugar beet plants. Nitrilase enzymes have been characterised in plants, bacteria and fungi and are thought to be important in detoxification of nitriles, utilisation of nitrogen and synthesis of plant hormones. We reveal that pinA is a NIT4-type nitrilase that catalyses the hydrolysis of beta-cyano-l-alanine, a nitrile common in the plant environment and an intermediate in the cyanide detoxification pathway in plants. In plants cyanide is converted to beta-cyano-l-alanine, which is subsequently detoxified to aspartic acid and ammonia by NIT4. In P. fluorescens SBW25 pinA is induced in the presence of beta-cyano-l-alanine, and the beta-cyano-l-alanine precursors cyanide and cysteine. pinA allows P. fluorescens SBW25 to use beta-cyano-l-alanine as a nitrogen source and to tolerate toxic concentrations of this nitrile. In addition, pinA is shown to complement a NIT4 mutation in Arabidopsis thaliana, enabling plants to grow in concentrations of beta-cyano-l-alanine that would otherwise prove lethal. Interestingly, over-expression of pinA in wild-type A. thaliana not only resulted in increased growth in high concentrations of beta-cyano-l-alanine, but also resulted in increased root elongation in the absence of exogenous beta-cyano-l-alanine, demonstrating that beta-cyano-l-alanine nitrilase activity can have a significant effect on root physiology and root development.