Diverse Sorghum bicolor accessions show marked variation in growth and transcriptional responses to arbuscular mycorrhizal fungi

Abstract

Sorghum is an important crop grown worldwide for feed and fibre. Like most plants, it has the capacity to benefit from symbioses with arbuscular mycorrhizal (AM) fungi, and its diverse genotypes likely vary in their responses. Currently, the genetic basis of mycorrhiza-responsiveness is largely unknown. Here, we investigated transcriptional and physiological responses of sorghum accessions, founders of a bioenergy nested association mapping panel, for their responses to four species of AM fungi.Transcriptome comparisons across four accessions identified mycorrhiza-inducible genes; stringent filtering criteria revealed 278 genes that show mycorrhiza-inducible expression independent of genotype and 55 genes whose expression varies with genotype. The latter suggests variation in phosphate transport and defence across these accessions. The mycorrhiza growth and nutrient responses of 18 sorghum accessions varied tremendously, ranging from mycorrhiza-dependent to negatively mycorrhiza-responsive. Additionally, accessions varied in the number of AM fungi to which they showed positive responses, from one to several fungal species. Mycorrhiza growth and phosphorus responses were positively correlated, whereas expression of two mycorrhiza-inducible phosphate transporters, SbPT8 and SbPT9, correlated negatively with mycorrhizal growth responses. AM fungi improve growth and mineral nutrition of sorghum, and the substantial variation between lines provides the potential to map loci influencing mycorrhiza responses.

Carbon for nutrient exchange between arbuscular mycorrhizal fungi and wheat varies according to cultivar and changes in atmospheric carbon dioxide concentration

“…AMF has previously been identified across cereal varieties (Hetrick, Wilson, & Cox, 1992;Lehnert et al, 2018;Watts-Williams et al, 2019). Such genotypic differences in growth resulting from AMF symbioses are likely to be linked not only to the receptivity to fungal colonization, but also to the physiological function of the AMF associations, particularly the degree to which the fungal symbionts represent a carbon sink (Walder et al, 2012)…”

“…AMF symbionts has been identified as sources of functional diversity in arbuscular mycorrhizal symbiosis (Johnson, Martin, et al, 2015;Watts-Williams et al, 2019). .…”

“…The functional response of plants to AMF colonization is highly diverse (Hoeksema et al, ) in terms of both inter‐ and intraspecificity (Johnson, Martin, Cairney, & Anderson, ; Jones & Smith, ; Mensah et al, ; Munkvold, Kjoller, Vestberg, Rosendahl, & Jakobsen, ; Watts‐Williams et al, ) and given the ubiquity of AMF in most agricultural soils, arable crops are far more likely to be mycorrhizal than nonmycorrhizal (Smith & Smith, ). As such, determining the conditions under which AMF positively influence crop nutrient uptake must remain a research priority.…”

Experimental system and image analysis software for high throughput phenotyping of mycorrhizal growth response inBrachypodium distachyon

“…Differences in host efficiency to acquire N and P from AM fungi could be one of them. Alternatively, AM fungi induce plant defense (Güimil et al ., 2005; Campos-Soriano et al ., 2012; Watts-Williams et al ., 2019) and trade-off between plant growth and defense are known (reviewed in Karasov et al ., 2017). Differences in level of host defense induction by AM fungi might explain difference in MGR.…”

“…However, there is host and symbiont genetic variability for plant growth stimulation by AM fungi in controlled conditions. For example, mycorrhizal growth response (MGR) can be either positive or negative in wheat (Hetrick & Wilson, 1992; Xavier & Germida, 1998; Lehnert et al ., 2018) and sorghum (Watts-Williams et al ., 2019). Very little is known about the genetic determinants that control MGR.…”