Role and mechanisms of callose priming in mycorrhiza-induced resistance

Abstract

Mycorrhizal plants display enhanced resistance to several pathogens. However, the molecular mechanisms regulating mycorrhiza-induced resistance (MIR) are still elusive. We aim to study the mechanisms underlying MIR against Botrytis cinerea and the role of callose accumulation during this process. Mycorrhizal tomato plants inoculated with Rhizoglomus irregularis displayed callose priming upon B. cinerea infection. The callose inhibitor 2-deoxy-d-glucose abolished MIR, confirming the relevance of callose in the bioprotection phenomena. While studying the mechanisms underlying mycorrhiza-induced callose priming, we found that mycorrhizal plants display an enhanced starch degradation rate that is correlated with increased levels of β-amylase1 transcripts following pathogen infection. Starch mobilization in mycorrhizal plants seems coordinated with the increased transcription of sugar transporter and invertase genes. Moreover, the expression levels of genes encoding the vesicular trafficking proteins ATL31 and SYP121 and callose synthase PMR4 were higher in the mycorrhizal plants and further boosted by subsequent pathogen infection. All these proteins play a key role in the priming of callose accumulation in Arabidopsis, suggesting that callose priming is an induced resistance mechanism conserved in different plant species. This evidence highlights the importance of sugar mobilization and vesicular trafficking in the priming of callose as a defence mechanism in mycorrhiza-induced resistance.

Regulation and Function of Defense-Related Callose Deposition in Plants

“…I3CA treatment increased ABA levels, which activates a starch amylase (BAM1) to trigger augmented callose deposition against P. cucumerina [ 37 ]. A similar role of ABA and starch metabolism has also been reported in mycorrhiza-induced callose priming in tomato plants upon infection by necrotrophic fungal pathogen B. cinerea [ 24 ]. Intriguingly, ABA can enhance or repress Flg22-induced callose deposition in Arabidopsis depending on growth conditions [ 35 ] ( Figure 1 A).…”

“…Furthermore, resistance-inducing chemicals including salicylic acid (SA), SA analog benzo(1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH), and the nonprotein amino acid BABA can augment depositions of pathogen-inducible callose [ 21 , 22 ]. It has also been recently reported that in tomato and wheat callose priming can be induced by Rhizophaus irregularis , a mycorrhizal fungus that can enhance resistance to several pathogens such as the necrotrophic fungal pathogen Botrytis cinerea in tomato [ 23 , 24 ].…”

“…Increased callose deposition is also associated with mycorrhiza-induced resistance [ 21 ]. In tomato plants, for example, mycorrhizal tomato plants inoculated with R. irregularis displayed callose priming upon B. cinerea infection in correlation with increased resistance to the necrotrophic fungal pathogen [ 24 ].…”

Genome-wide Association Studies Reveal Important Candidate Genes for theBacillus pumilusTUAT-1-Arabidopsis thalianaInteraction

“…In our study, we also found a potential PGPB interaction gene, ERF9, which is an ethylene response factor that negatively regulates plant defense (Huang 2016). In addition, the pair of co-regulated genes ATMIN7 and GSL05 are also related with the plant immune response (Deslandes 2012 andSanmartín 2020). Another important finding is the pair of co-expressed genes AL6 and UBP14, which are involved in the phosphate starvation response (Chandrika 2013 and.…”

Roots drive oligogalacturonide‐induced systemic immunity in tomato

“…The fungus was cultivated in potato dextrose agar plates, supplemented with freeze‐dried tomato leaves. Three weeks later, B. cinerea spores were collected from plates in 0.5X potato dextrose broth as previously described (Sanmartín et al, 2020).…”