Effect of the expression of Escherichia coli fhuA gene in Rhizobium sp. IC3123 and ST1 in planta: Its role in increased nodule occupancy and function in pigeon pea

Isolation and Characterization of Nodule-AssociatedExiguobacterium sp. from the Root Nodules ofFenugreek(Trigonella foenum-graecum) and Their Possible Role in Plant Growth Promotion

“…Thus it was interesting to see whether the siderophores produced by the NAB and the rhizospheric isolates were being cross-utilized by the S. meliloti . Our earlier studies have shown rhizobial growth stimulation in presence of exogenously supplied siderophores that it is able to utilize [ 28 ] and we have shown that rhizobial strains when transformed with the ferrichrome siderophore receptor gene caused growth stimulation in the presence of Fe 3+ [ 44 ] and also caused the plant growth promotion under both sterile and nonsterile soil conditions in lab [ 45 ]; we have also demonstrated the plant growth promoting effect of the siderophore produced by the Bacilli sp . on the rhizobial bioinoculants strains of C. cajan [ 26 ].…”

Engineering Rhizobial Bioinoculants: A Strategy to Improve Iron Nutrition

“…Most of the rhizobial strains fail to utilize ferrichrome and other related hydroxamate type siderophores and are at competitive disadvantage in iron sufficiency [ 59 , 77 ]. Heterologous receptors like ( fhuA ) from Escherichia coli or ( fegA ) from a B. japonicum strain that are proficient at utilizing ferrichrome have been expressed in rhizobial strains nodulating Cajanus cajan [ 59 , 78 , 79 ] and ground nut [ 80 ] plants. Engineering rhizobial strains by incorporating genes for multiple iron-siderophore receptors potentially increased the suite of ferricsiderophores that they could utilize.…”

“…Rhizospheric colonization and survival was also increased with transformants as compared to their parent under both autoclaved and unautoclaved conditions. Thus, it was demonstrated that increased survival of the strains does improve their nodule occupancy on C. cajan which in turn had positive effects on plant growth [ 78 ]. Similarly fegA -bearing strain when inoculated in unautoclaved soils with indigenous rhizobia (that could nodulate) showed better competitive nodulation ability [ 79 ].…”

“…Successful strategies in this regard are as follows: (1) construction of a chimeric Nif HDK operon under the strong NifHc promoter and expression in PHB negative mutants of R. etli [ 123 ], (2) construction of an acid-tolerant R. leguminosarum bv. trifolii strain [ 124 ], (3) expression of ACC deaminase gene in S. meliloti [ 125 ], (4) overexpression of putA [ 126 ], (5) overexpression of trehalose 6-phosphate synthase [ 127 ], (6) overexpression of rosR and pssR [ 128 ], (7) heterologous expression of ferrichrome siderophore receptor gene fegA and fhuA [ 78 – 80 ], and (8) overproduction of the adhesion rap1 [ 129 ]. Of these, the strategy of Peralta et al [ 123 ] explained that R. etli strains with the chimeric nitrogenase construct assayed in greenhouse experiments had increased nitrogenase activity (58% on average), plant weight (32% on average), N content in plants (15% at 32 days after inoculation), and most importantly higher seed yield (36% on average), higher N content (25%), and higher N yield (72% on average) in seeds.…”

“…ST1 was inhibited slightly in the presence of ferrichrome under lab conditions and also under natural soil conditions, but the expression of fhuA genes into Rhizobium sp. ST1 increased its rhizospheric stability, which was evident by its increase in nodule occupancy on the C. cajan plants [ 59 , 78 , 149 ]. The fegA gene with its native promoter when subcloned and transferred into Mesorhizobium sp.…”