Legume-rhizobia signal exchange: promiscuity and environmental effects

Abstract

Although signal exchange between legumes and their rhizobia is among the best-known examples of this biological process, most of the more characterized data comes from just a few legume species and environmental stresses. Although a relative wealth of information is available for some model legumes and some of the major pulses such as soybean, little is known about tropical legumes. This relative disparity in current knowledge is also apparent in the research on the effects of environmental stress on signal exchange; cool-climate stresses, such as low-soil temperature, comprise a relatively large body of research, whereas high-temperature stresses and drought are not nearly as well understood. Both tropical legumes and their environmental stress-induced effects are increasingly important due to global population growth (the demand for protein), climate change (increasing temperatures and more extreme climate behavior), and urbanization (and thus heavy metals). This knowledge gap for both legumes and their environmental stresses is compounded because whereas most temperate legume-rhizobia symbioses are relatively specific and cultivated under relatively stable environments, the converse is true for tropical legumes, which tend to be promiscuous, and grow in highly variable conditions. This review will clarify some of this missing information and highlight fields in which further research would benefit our current knowledge.

Policing the legume-Rhizobium symbiosis: a critical test of partner choice

“…Instead, an extensive signalling process 35–37 between legumes and their rhizobial partners can impose a high degree of selectivity on the relationship 36, 38, 39 , although the degree of selectivity varies greatly among hosts 39 . There are two explanations for this selectivity that are commonly proposed and are not mutually exclusive.…”

Co‐introduction vs ecological fitting as pathways to the establishment of effective mutualisms during biological invasions

“…Checcucci et al ., ). This could reflect the existence of strong host control of the interaction through mechanisms like partner choice (Lira et al ., ) or sanctioning (Kiers et al ., ). However, partner choice is not perfect, as nodules often house ineffective bacteria, with recent evidence suggesting that, in some instances, nodules can be colonized by a range of non‐N‐fixing rhizobia or even nonrhizobial bacteria (Birnbaum et al ., ; Busby et al ., ; Checcucci et al ., ).…”

“…Checcucci et al, 2016). This could reflect the existence of strong host control of the interaction through mechanisms like partner choice (Lira et al, 2015) or sanctioning (Kiers et al, 2003). However, partner choice is not perfect, as nodules often house ineffective bacteria, with recent evidence suggesting that, in some instances, nodules can be colonized by a range of non-N-fixing rhizobia or even nonrhizobial bacteria ( The performance (yellow, high; blue, low) is visualized on the plane of coevolution (shared phylogenetic history between the invading legume and the rhizobia with which it interacts in the invasion range) and interaction specialization (ranging from interactions between specialist legumes and specialist rhizobia to those between generalist legumes and generalist rhizobia).…”

The ecological role of volatile mediated interactions belowground

“…Several reports describe the chemical dialog between microbes, plants, and other organisms by the exchange of soluble compounds (Badri et al 2009;Lira Jr et al 2015;Song et al 2015a;Liu et al 2016). Most of the studies reporting mVOCs-mediated communication belowground focus on the uni-directional responses and only a few studies reported on bidirectional mVOCs-mediated interactions.…”