Effect of GFP tagging of Paenibacillus polymyxa P2b-2R on its ability to promote growth of canola and tomato seedlings

Abstract

Green fluorescent protein (GFP) is used extensively in detecting internal tissue colonization by endophytes of various genera, but our knowledge about the effects of GFP tagging is very limited. We wanted to determine if a GFP-labeled derivative of Paenibacillus polymyxa P2b-2R (P2b-2Rgfp) would fix N and promote growth of two important crop species, canola and tomato, in ways similar to the wild-type P2b-2R. To evaluate this, canola and tomato seeds were inoculated with P2b-2R or P2b-2Rgfp and grown for 40 days in sterile conditions inside a growth chamber. P2b-2Rgfp-inoculated seedlings were compared with uninoculated controls and P2b-2Rinoculated seedlings, after 20, 30, and 40 days of inoculation for biological N fixation (15N dilution) and growth response (length and biomass). The entire experiment was repeated to confirm the treatment effects. It was found that canola seedlings inoculated with P2b-2Rgfp had 118% more biomass than controls and 69% more biomass than P2b-2Rtreated seedlings; were 69% longer than controls and 37% longer than seedlings inoculated with P2b-2R; and derived 22% of their N from the atmosphere (6% more than P2b-2R-treated canola seedlings). This shows that canola seedlings responded remarkably to P2b-2Rgfp inoculation, even better than wild-type P2b-2R inoculation. But, in the case of tomato, P2b-2Rgfp-inoculated seedlings were statistically analogous to the P2b-2R-inoculated seedlings in terms of growth promotion and N fixation. Seedlings inoculated with either P2b-2Rgfp or P2b-2R were nearly 40% longer than controls, assimilated nearly 90%more biomass than controls, and fixed nearly 17% of N from the atmosphere. To the best of our knowledge, results of canola represent the very first evidence that transformation of an endophyte by GFP can significantly enhance its plant growth-promoting efficacy. Contrasting results of tomato suggest that the positive effects ofGFP tagging of P2b-2R might vary depending on the host plant.