Improvement of phosphate solubilization and Medicago plant yield by an indole-3-acetic acid-overproducing strain of Sinorhizobium meliloti.
Nitrogen (N) and phosphorus (P) are the most limiting factors for plant growth. Some microorganisms improve the uptake and availability of N and P, minimizing chemical fertilizer dependence. It has been published that the RD64 strain, a Sinorhizobium meliloti 1021 strain engineered to overproduce indole-3-acetic acid (IAA), showed improved nitrogen fixation ability compared to the wild-type 1021 strain. Here, we present data showing that RD64 is also highly effective in mobilizing P from insoluble sources, such as phosphate rock (PR). Under P-limiting conditions, the higher level of P-mobilizing activity of RD64 than of the 1021 wild-type strain is connected with the upregulation of genes coding for the high-affinity P transport system, the induction of acid phosphatase activity, and the increased secretion into the growth medium of malic, succinic, and fumaric acids. Medicago truncatula plants nodulated by RD64 (Mt-RD64), when grown under P-deficient conditions, released larger amounts of another P-solubilizing organic acid, 2-hydroxyglutaric acid, than plants nodulated by the wild-type strain (Mt-1021). It has already been shown that Mt-RD64 plants exhibited higher levels of dry-weight production than Mt-1021 plants. Here, we also report that P-starved Mt-RD64 plants show significant increases in both shoot and root fresh weights when compared to P-starved Mt-1021 plants. We discuss how, in a Rhizobium-legume model system, a balanced interplay of different factors linked to bacterial IAA overproduction rather than IAA production per se stimulates plant growth under stressful environmental conditions and, in particular, under P starvation.
Institute of Genetics and Biophysics Adriano Buzzati Traverso, Castellino, 80131 Naples, Italy.
Carmen
C
Bianco
Roberto
R
Defez
D018533:Biomass; D005650:Fumarates / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D046913:Medicago truncatula / Q000254:growth & development* / Q000378:metabolism* / Q000382:microbiology; D010710:Phosphates / Q000378:metabolism*; D053204:Root Nodules, Plant / Q000382:microbiology; D016962:Sinorhizobium meliloti / Q000201:enzymology* / Q000378:metabolism*; D019802:Succinic Acid / Q000378:metabolism
D005650:Fumarates; D007210:Indoleacetic Acids; D008293:Malates; D010710:Phosphates; C030737:indoleacetic acid; C030298:malic acid; C032005:fumaric acid; D019802:Succinic Acid