Francis Isolde M, Stes Elisabeth, Zhang Yucheng, Rangel Diana, Audenaert Kris, Vereecke Danny
Department of Biology, California State University Bakersfield, Bakersfield, CA 93311, USA.
Department of Plant Systems Biology, VIB, 9052 Gent, Belgium; Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Gent, Belgium.
N Biotechnol. 2016 Sep 25;33(5 Pt B):706-717. doi: 10.1016/j.nbt.2016.01.009. Epub 2016 Feb 11.
Rhodococcus fascians is a phytopathogenic Gram-positive Actinomycete with a very broad host range encompassing especially dicotyledonous herbaceous perennials, but also some monocots, such as the Liliaceae and, recently, the woody crop pistachio. The pathogenicity of R. fascians strain D188 is known to be encoded by the linear plasmid pFiD188 and to be dictated by its capacity to produce a mixture of cytokinins. Here, we show that D188-5, the nonpathogenic plasmid-free derivative of the wild-type strain D188 actually has a plant growth-promoting effect. With the availability of the genome sequence of R. fascians, the chromosome of strain D188 was mined for putative plant growth-promoting functions and the functionality of some of these activities was tested. This analysis together with previous results suggests that the plant growth-promoting activity of R. fascians is due to production of plant growth modulators, such as auxin and cytokinin, combined with degradation of ethylene through 1-amino-cyclopropane-1-carboxylic acid deaminase. Moreover, R. fascians has several functions that could contribute to efficient colonization and competitiveness, but there is little evidence for a strong impact on plant nutrition. Possibly, the plant growth promotion encoded by the D188 chromosome is imperative for the epiphytic phase of the life cycle of R. fascians and prepares the plant to host the bacteria, thus ensuring proper continuation into the pathogenic phase.
fascians是一种植物致病性革兰氏阳性放线菌，宿主范围非常广泛，尤其包括双子叶多年生草本植物，但也包括一些单子叶植物，如百合科植物，以及最近发现的木本作物阿月浑子。已知fascians菌株D188的致病性由线性质粒pFiD188编码，并由其产生细胞分裂素混合物的能力决定。在这里，我们表明，野生型菌株D188的无致病性质粒衍生物D188-5实际上具有促进植物生长的作用。随着fascians基因组序列的获得，我们对菌株D188的染色体进行了挖掘，以寻找假定的促进植物生长的功能，并对其中一些活性的功能进行了测试。该分析与先前的结果共同表明，fascians促进植物生长的活性是由于植物生长调节剂如生长素和细胞分裂素的产生，以及通过1-氨基环丙烷-1-羧酸脱氨酶对乙烯的降解。此外，fascians具有多种有助于有效定殖和竞争力的功能，但几乎没有证据表明其对植物营养有强烈影响。可能，D188染色体编码的植物生长促进作用对于fascians生命周期的附生阶段至关重要，并使植物为容纳细菌做好准备，从而确保顺利进入致病阶段。
