Michiels J, Pelemans H, Vlassak K, Verreth C, Vanderleyden J
F. A. Janssens Laboratory of Genetics, Catholic University of Leuven, Heverlee, Belgium.
Mol Plant Microbe Interact. 1995 May-Jun;8(3):468-72. doi: 10.1094/mpmi-8-0468.
DNA sequence analysis of a 1.4-kb SalI-HindIII segment located approximately 2 kb upstream of the Rhizobium leguminosarum bv. phaseoli syrM gene revealed the presence of an open reading frame (ORF3) encoding a putative 295-amino acid polypeptide with a molecular mass of 33,401 Da. ORF3 is homologous to a R. fredii host-inducible gene. The proteins encoded by R. l. bv. phaseoli ORF3 and by the R. fredii host-inducible gene share 37% sequence identity. In contrast to the R. fredii host-inducible gene, expression of ORF3 is not induced in the presence of Phaseolus vulgaris root exudates or by specific flavonoids, able to induce nodulation genes in R. l. bv. phaseoli. A R. l. bv. phaseoli ORF3 mutant was constructed by site-directed deletion/replacement mutagenesis. This mutant strain is not affected in symbiotic nitrogen fixation but exhibits a delay in nodulation on Phaseolus vulgaris. Moreover, this mutant was shown to be defective in competition for nodulation.
对位于菜豆根瘤菌（Rhizobium leguminosarum bv. phaseoli）syrM基因上游约2 kb处的一个1.4 kb的SalI-HindIII片段进行DNA序列分析，结果显示存在一个开放阅读框（ORF3），其编码一个推定的295个氨基酸的多肽，分子量为33,401 Da。ORF3与费氏中华根瘤菌（R. fredii）的一个宿主诱导基因同源。菜豆根瘤菌ORF3和费氏中华根瘤菌宿主诱导基因所编码的蛋白质具有37%的序列同一性。与费氏中华根瘤菌宿主诱导基因不同，在菜豆根分泌物存在的情况下，或者在能够诱导菜豆根瘤菌结瘤基因的特定类黄酮存在的情况下，ORF3的表达不会被诱导。通过定点缺失/置换诱变构建了菜豆根瘤菌ORF3突变体。该突变菌株在共生固氮方面没有受到影响，但在菜豆上结瘤出现延迟。此外，该突变体在结瘤竞争方面表现出缺陷。
