On the outside looking in: roles of endogenous and exogenous strigolactones

Abstract

Summary A collection of small molecules called strigolactones (SLs) act as both endogenous hormones to control plant development and as ecological communication cues between organisms. SL signalling overlaps with that of a class of smoke‐derived compounds, karrikins (KARs), which have distinct yet overlapping developmental effects on plants. Although the roles of SLs in shoot and root development, in the promotion of arbuscular mycorrhizal (AM) fungal branching and in parasitic plant germination have been well characterized, recent data have illustrated broader roles for these compounds in the rhizosphere. Here, we review the known roles of SLs in development, growth of AM fungi and germination of parasitic plants to develop a framework for understanding the use of SLs as molecules of communication in the rhizosphere. It appears, for example, that there are many connections between SLs and phosphate utilization. Low phosphate levels regulate SL metabolism and, in turn, SLs sculpt root and shoot architecture to coordinate growth and optimize phosphate uptake from the environment. Plant‐exuded SLs attract fungal symbionts to deliver inorganic phosphate (Pi) to the host. These and other examples suggest the boundary between exogenous and endogenous SL functions can be easily blurred and a more holistic view of these small molecules is likely to be required to fully understand SL biology. Related to this, we summarize and discuss evidence for a primitive role of SLs in moss as a quorum sensing‐like molecule, providing a unifying concept of SLs as endogenous and exogenous signalling molecules.

Characterization of growth and development of sorghum genotypes with differential susceptibility toStriga hermonthica

“…Consequently, SRN39 shows resistance to Striga in the field as opposed to the highly susceptible SQR (Gobena et al ., 2017; Mohamed et al ., 2003). The predominant role of strigolactone within root exudates, however, is recruitment of arbuscular mycorrhiza fungi, while parasitic plants co-opted strigolactone signalling into their host plant-dependent lifecycle (Aquino et al ., 2020). Increasing evidence suggests that strigolactones also govern assembly of the rhizosphere microbiome (reviewed in (Aliche et al ., 2020).…”

“…Strigolactones also act as an endogenous plant hormone and as such regulate plant root and shoot architecture (Aquino et al ., 2020). Strigolactones repress shoot branching (Gomez-Roldan et al ., 2008; Umehara et al ., 2008) and promote secondary growth of the stem (Agusti et al ., 2011).…”

Allelopathic Activity of Strigolactones on the Germination of Parasitic Plants and Arbuscular Mycorrhizal Fungi Growth

“…A significant number of recent studies on SLs focuses on this issue, such as evaluating the role of SLs production by rootstocks in grafted grapevine plants [54]. Detailed descriptions of endogenous roles of SLs and their mechanisms are available in recent reviews [55,56].…”

“…Arbuscular mycorrhizal fungi (AMF) are a class of beneficial microorganisms widely distributed in soils, forming symbiotic associations with land plants (70-80% of species) for more than 460 million years [2,55]. In this symbiotic interaction, AMF supplies water and nutrients from the soil (beyond the root rhizosphere) to the host plant; and the host provides photoassimilates (carbohydrates produced by photosynthesis in the leaves [79]) to the AMF [80].…”

Plant hormone functions and interactions in biological systems

“…SLs regulate plant growth and development but also act as communication tools between plants and other organisms, such as parasitic plants and microbes that reside in the rhizosphere. Aquino et al (2020) provide an up‐to‐date review of the functions of SLs as endogenous and exogenous signal molecules in the direct and indirect regulation of plant growth and development. They also discuss the roles of SLs in the regulation of colonization of moss.…”