Common and divergent shoot–root signalling in legume symbioses

Abstract

SummaryThe role of shoot-root signals in the control of nodulation and arbuscular mycorrhizal (AM) development were examined in the divergent legume species pea and blue lupin. These species were chosen as pea can host both symbionts, whereas lupin can nodulate but has lost the ability to form AM.Intergeneric grafts between lupin and pea enabled examination of key long-distance signals in these symbioses. The role of strigolactones, auxin and elements of the autoregulation of nodulation (AON) pathway were investigated. Grafting studies were combined with loss-offunction mutants to monitor symbioses (nodulation, AM) and hormone effects (levels, gene expression and application studies).Lupin shoots suppress AM colonization in pea roots, in part by downregulating strigolactone exudation involving reduced expression of the strigolactone biosynthesis gene PsCCD8. By contrast, lupin shoots enhance pea nodulation, independently of strigolactones, possibly due to a partial incompatibility in AON shoot-root signalling between pea and lupin.This study highlights that nodulation and AM symbioses can be regulated independently and this may be due to long-distance signals, a phenomenon we were able to uncover by working with divergent legumes. We also identify a role for strigolactone exudation in determining the status of non-AM hosts.

Nutrient demand and fungal access to resources control the carbon allocation to the symbiotic partners in tripartite interactions of Medicago truncatula

“…The reduced AM root colonization likely caused a reduced exploration of the HC to which the 15 N was supplied, and the low expression of A suppression of the other root symbiont by a prior colonization of the root system by AM fungi or rhizobia has also been reported by other authors (Catford et al, 2003;Catford et al, 2006;Mortimer et al, 2013;Sakamoto, Ogiwara, & Kaji, 2013). It is well established that a prior exposure to rhizobia can limit the subsequent formation of root nodules on the root system (Ferguson et al, 2010;Foo, Heynen, & Reid, 2016). This process is known as autoregulation of nodulation and involves a root-derived signal that is perceived by a…”

“…A suppression of the other root symbiont by a prior colonization of the root system by AM fungi or rhizobia has also been reported by other authors (Catford et al, ; Catford et al, ; Mortimer et al, ; Sakamoto, Ogiwara, & Kaji, ). It is well established that a prior exposure to rhizobia can limit the subsequent formation of root nodules on the root system (Ferguson et al, ; Foo, Heynen, & Reid, ). This process is known as autoregulation of nodulation and involves a root‐derived signal that is perceived by a CLAVATA1‐like leucine rich repeat receptor kinase ( MtSUNN in Medicago ) and triggers the production of a shoot‐derived inhibitor that suppresses further nodule development (Reid, Ferguson, & Gresshoff, ; Reid, Ferguson, Hayashi, et al, ).…”

Gibberellins promote nodule organogenesis but inhibit the infection stages of nodulation

“…cDNA was diluted, and duplicate, real-time PCRs were performed in a Rotor Gene 2000 (Corbett, USA) using the SensiFAST™ SYBR ® Hi-ROX Kit (Bioline) and 100–200 pmol of a primer pair. New primer pairs for genes analysed in this study are given in Supplementary Table S1 , and previously published primer pairs are as follows: PsGA2-ox-2 , PsGA3-ox , and PsGA20-ox ( Foo et al , 2006 ), PsENOD12a and PsENOD40 ( Foo et al , 2016 a ), and the housekeeping gene PsACTIN ( Foo et al , 2005 ). Standard curves were created for each gene using serially diluted plasmids containing cloned fragments of each amplicon, and plasmids were sequenced to verify specificity.…”

“…5C and D , lupin seeds were nicked and treated at the time of planting with either 10 µl of ethanol (control), 10 µg of GA 3 , and/or 10 µg of paclobutrazol (PAC; Sigma Aldrich Pty. Ltd, Australia) in 10 µl of ethanol, planted and inoculated with appropriate bacteria as described by Foo et al , (2016 a ), and nodule size was recorded at 28 d as described by Foo et al (2016 b ).…”

The role of CLV signalling in the negative regulation of mycorrhizal colonisation and nitrogen response of tomato

“…Studies in legumes indicate at least some of the genetic elements in autoregulation of nodulation (AON) overlap with elements of autoregulation of mycorrhizae (AOM) but have also highlighted some important differences (e.g. Catford, 2003;Foo et al, 2016;Müller et al, 2019).…”