Quantitative analyses of BNF and plant growth promotion
demonstrated that plant and bacterial genotypes are important
factors in controlling the efficiency of the association
(Carvalho et al., 2011). In this context, one challenge in this
area is the determination of the best combination of diazotrophic
bacteria and plant varieties to obtain the maximum
benefit from this association in agriculture. A huge effort
should be made to understand the molecular and genetic factors
controlling all steps of the association: recognition, colonization,
N fixation, and plant growth promotion. Several
advances came from genomic approaches, and integrative
gene expression maps are being generated for some plant species
colonized with associative and endophytic diazotrophic
bacteria. Possible regulatory mechanisms involved were identified,
and functional analyses are now necessary. Also, it is
important to determine common regulatory pathways governing
a successful association with diazotrophic bacteria, as
well as those specific to particular plant–bacteria genotypes