PAL‐mediated SA biosynthesis pathway contributes to nematode resistance in wheat

Abstract

Summary The pathogen cereal cyst nematode (CCN) is deleterious to Triticeae crops and is a threat to the global crop yield. Accession no. 1 of Aegilops variabilis, a relative of Triticum aestivum (bread wheat), is highly resistant to CCN. Our previous study demonstrated that the expression of the phenylalanine ammonia lyase (PAL) gene AevPAL1 in Ae. variabilis is strongly induced by CCN. PAL, the first enzyme of phenylpropanoid metabolism, is involved in abiotic and biotic stress responses. However, its role in plant–CCN interaction remains unknown. In the present study, we proved that AevPAL1 helps to confer CCN resistance through affecting the synthesis of salicylic acid (SA) and downstream secondary metabolites. The silencing of AevPAL1 increased the incidence of CCN infection in roots and decreased the accumulation of SA and phenylalanine (Phe)‐derived specialized metabolites. The exogenous pre‐application of SA also improved CCN resistance. Additionally, the functions of PAL in phenylpropanoid metabolism correlated with tryptophan decarboxylase (TDC) functioning in tryptophan metabolism pathways. The silencing of either AevPAL1 or AevTDC1 exhibited a concomitant reduction in the expression of both genes and the contents of metabolites downstream of PAL and TDC. These results suggested that AevPAL1, possibly in coordination with AevTDC1, positively contributes to CCN resistance by altering the downstream secondary metabolites and SA content in Ae. variabilis. Moreover, AevPAL1 overexpression significantly enhanced CCN resistance in bread wheat and did not exhibit significant negative effects on yield‐related traits, suggesting that AevPAL1 is valuable for the genetic improvement of CCN resistance in bread wheat.

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

“…In transgenic tobacco, reduction in lesion size and the number has also been witnessed in plants with PAL over-expression after getting infected with P. syringae. Similarly, bread wheat exhibited PAL gene AevPAL1 confers resistance to cereal cyst nematode by affecting the synthesis of salicylic acid and downstream secondary metabolites (Zhang et al 2021). These studies indicate that PAL over-expression in plants provides disease resistance.…”

Phylogenomic analysis of phenylalanine ammonia-lyase (PAL) multigene family and their differential expression analysis in wheat (Triticum aestivum L.) suggested their roles during different stress responses

“…The expression levels of PAL genes were up-regulated in wheat cultivars resistant to Fusarium graminearum (Golkari et al, 2009). Overexpression of Aegilops variabilis PAL (AevPAL1) significantly enhanced cereal cyst nematode resistance in bread wheat (Zhang et al, 2021). Although these studies further showed that the PAL genes played an important role in the process of stress defense, its comprehensive information and functions under biotic stress in wheat remains unclear.…”

Monitoring of Host Suitability and Defense-Related Genes in Wheat to Bipolaris sorokiniana

“…glycine, but not in the susceptible cultivar [71]. The silencing of PAL in wheat reduced aphid and nematode resistance [72], while PAL-RNAi in Brachypodium increased susceptibilities to the fungal pathogens F. culmorum and Magnaporthe oryzae [73]. However, the suppression of some PAL genes had no significant effect on plant resistance to F. graminearum [35].…”