AUTHOR=Tsyganov Viktor E. , Tsyganova Anna V. , Gorshkov Artemii P. , Seliverstova Elena V. , Kim Viktoria E. , Chizhevskaya Elena P. , Belimov Andrey A. , Serova Tatiana A. , Ivanova Kira A. , Kulaeva Olga A. , Kusakin Pyotr G. , Kitaeva Anna B. , Tikhonovich Igor A. 

TITLE=Efficacy of a Plant-Microbe System: Pisum sativum (L.) Cadmium-Tolerant Mutant and Rhizobium leguminosarum Strains, Expressing Pea Metallothionein Genes PsMT1 and PsMT2, for Cadmium Phytoremediation

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00015

DOI=10.3389/fmicb.2020.00015

ISSN=1664-302X

ABSTRACT=<p>Two transgenic strains of <italic>Rhizobium leguminosarum</italic> bv. <italic>viciae</italic>, 3841-PsMT1 and 3841-PsMT2, were obtained. These strains contain the genetic constructions <italic>nifH-PsMT1</italic> and <italic>nifH-PsMT2</italic> coding for two pea (<italic>Pisum sativum</italic> L.) metallothionein genes, <italic>PsMT1</italic> and <italic>PsMT2</italic>, fused with the promoter region of the <italic>nifH</italic> gene. The ability of both transgenic strains to form nodules on roots of the pea wild-type SGE and the mutant SGECd<sup>t</sup>, which is characterized by increased tolerance to and accumulation of cadmium (Cd) in plants, was analyzed. Without Cd treatment, the wild type and mutant SGECd<sup>t</sup> inoculated with <italic>R. leguminosarum</italic> strains 3841, 3841-PsMT1, or 3841-PsMT2 were similar histologically and in their ultrastructural organization of nodules. Nodules of wild-type SGE inoculated with strain 3841 and exposed to 0.5 μM CdCl<sub>2</sub> were characterized by an enlarged senescence zone. It was in stark contrast to Cd-treated nodules of the mutant SGECd<sup>t</sup> that maintained their proper organization. Cadmium treatment of either wild-type SGE or mutant SGECd<sup>t</sup> did not cause significant alterations in histological organization of nodules formed by strains 3841-PsMT1 and 3841-PsMT2. Although some abnormalities were observed at the ultrastructural level, they were less pronounced in the nodules of strain 3841-PsMT1 than in those formed by 3841-PsMT2. Both transgenic strains also differed in their effects on pea plant growth and the Cd and nutrient contents in shoots. In our opinion, combination of Cd-tolerant mutant SGECd<sup>t</sup> and the strains 3841-PsMT1 or 3841-PsMT2 may be used as an original model for study of Cd tolerance mechanisms in legume-rhizobial symbiosis and possibilities for its application in phytoremediation or phytostabilization technologies.</p>