Isolation and characterization of rhizobitoxine mutants of Bradyrhizobium japonicum
Isolation and characterization of rhizobitoxine mutants of Bradyrhizobium japonicum
复制标题
日本慢生根瘤菌根瘤菌素突变体的分离和鉴定
DOI：
10.1128/jb.174.11.3467-3473.1992
复制
发表时间：
1992
影响因子：
3.2
通讯作者：
N. Peters
中科院分区：
文献类型：
--
作者：
X. Ruan;N. Peters
为探讨根瘤菌毒素在慢生根瘤菌-豆科植物共生中的作用，利用在培养中不能合成根瘤菌毒素的日本芽孢杆菌USDA61分离出了11个根瘤菌毒素突变体。每个突变体对大豆、豇豆、豇豆和甘氨酸大豆具有原生营养和共生效应。根霉毒素突变体在植物的黄化表型和根霉毒素产量方面存在差异。正如预期的那样，一组突变体不能在植物中产生毒素，导致没有褪绿。另一组突变体在所有大豆品种上引起严重的黄化。令人惊讶的是，这组突变体在大豆根瘤中比野生型菌株产生更多的根瘤素。这种表型只在大豆上观察到，而在其他寄主如豇豆、豇豆或大豆上没有观察到。其余的突变体在植物中都产生根瘤菌毒素，但它们产生的毒素量和它们在大豆植物中引起的黄化程度各不相同。对突变体的生化分析表明，一个突变体不能合成丝氨酸醇，丝氨酸醇被认为是根瘤菌毒素生物合成的中间分子。利用这些突变体，发现根瘤素对rj1大豆的结瘤无明显作用。近年来研究发现，抑制乙烯生物合成可使梅利罗蒂根瘤菌克服硝酸盐对苜蓿根瘤形成的抑制作用。由于根霉毒素也抑制乙烯生物合成，我们测试了在植物中积累高水平毒素的突变体克服硝酸盐对大豆根瘤形成抑制的能力，发现在硝酸盐的存在下，野生型和突变株诱导的根瘤形成同样受到抑制。
To explore the role of rhizobitoxine in Bradyrhizobium-legume symbiosis, 11 rhizobitoxine mutants of B. japonicum USDA61 were isolated on the basis of their inability to synthesize the toxin in culture. Each mutant is prototrophic and symbiotically effective on soybean, cowpea, siratro, and Glycine soja. The rhizobitoxine mutants differ in their chlorosis phenotypes and rhizobitoxine production in planta. As expected, one group of mutant fail to make toxin in planta, resulting in the absence of chlorosis. Another group of mutants causes severe chlorosis on all cultivars of soybean tested. Surprisingly, this group of mutants makes more rhizobitoxine in soybean nodules than the wild-type strain does. This phenotype is only observed on soybean and not on other hosts such as cowpea, siratro, or G. soja. The remaining mutants all produce rhizobitoxine in planta but vary in the amount of toxin they produce and the severity of chlorosis they induce in soybean plants. Biochemical analysis of mutants demonstrates that one mutant is unable to synthesize serinol, a molecule hypothesized to be an intermediate in rhizobitoxine biosynthesis. By using these mutants, it was found that rhizobitoxine plays no apparent role in the nodulation of rj1 soybeans. Recently, it was found that inhibition of ethylene biosynthesis allows Rhizobium meliloti to overcome nitrate inhibition of nodule formation on alfalfa. Because rhizobitoxine also inhibits ethylene biosynthesis, we tested the ability of mutants which accumulate high levels of toxin in planta to overcome nitrate inhibition of nodule formation on soybean plants and found that the nodule formation induced by the wild type and that induced by mutant strains were equally suppressed in the presence of nitrate.