Cell Biology Of Nodule Infection And Development

Abstract

The symbiosis between legumes and nodule-forming soil bacteria is fascinating for ecological, agricultural, evolutionary, physiological, and developmental reasons. The symbiosis culminates in the formation of a highly organized plant organ, the root nodule, with plant cells invaded by bacteria. The N2-fixing root nodule is thereby a paradigm for plant developmental processes and plant-microbe interactions. The nodule creates a micro-aerobic niche for N2 fixation, protecting the bacterial nitrogenase from inactivation by O2. Under favorable conditions and with limited soil nitrogen, the root system may carry hundreds of nodules with infected cells packed with thousands of N2-fixing bacteria. Although N2 fixation benefits the host plant, it is very unusual that an organism can tolerate the constant presence of microbes and at such a high concentration. This review focuses on two aspects of the symbiosis, namely, organ formation and plant cell infection.