Microbial signaling and plant growth promotion

The rhizosphere offers a complex microhabitat where root exudates provide a diverse mixture of organic compounds that are used as nutrients or signals by the soil microbial population. On the other hand, these soil microorganisms produce compounds that directly or indirectly assist in plant growth promotion. The widely recognized mechanisms of plant growth promotion are biofertilization, production of phytohormones, suppression of diseases through biocontrol, induction of disease resistance and production of volatile signal compounds. During the past few decades our understanding of the interaction between rhizobacteria and plants has expanded enormously and this has resulted in application of microbial products used as crop inoculants (as biofertilizers), for increased crop biomass and disease suppression. However, this plant-microbe interaction is affected by adverse environmental conditions, and recent work has suggested that inoculants carrying plant-to-bacteria or bacteria-to-plant signals can overcome this and promote plant productivity under stressful environmental conditions. Very recent work has also shown that some plant growth-promoting rhizobacteria secrete novel signaling molecules that also promote plant growth. The use of rhizobacterial signaling in promoting plant growth offers a new window of opportunity, especially when we are looking at plants to provide biofuels and novel bioproducts. Developing technologies that can enhance plant growth and productivity is imperative.