Comparing transcriptional responses to Fusarium crown rot in wheat and barley identified an important relationship between disease resistance and drought tolerance

Transcriptomic insights into shared responses to Fusarium crown rot infection and drought stresses in bread wheat (Triticum aestivum L.)

KEY MESSAGE

Shared changes in transcriptomes caused by Fusarium crown rot infection and drought stress were investigated based on a single pair of near-isogenic lines developed for a major locus conferring tolerance to both stresses. Fusarium crown rot (FCR) is a devastating disease in many areas of cereal production worldwide. It is well-known that drought stress enhances FCR severity but possible molecular relationship between these two stresses remains unclear. To investigate their relationships, we generated several pairs of near isogenic lines (NILs) targeting a locus conferring FCR resistance on chromosome 2D in bread wheat. One pair of these NILs showing significant differences between the two isolines for both FCR resistance and drought tolerance was used to investigate transcriptomic changes in responsive to these two stresses. Our results showed that the two isolines likely deployed different strategies in dealing with the stresses, and significant differences in expressed gene networks exist between the two time points of drought stresses evaluated in this study. Nevertheless, results from analysing Gene Ontology terms and transcription factors revealed that similar regulatory frameworks were activated in coping with these two stresses. Based on the position of the targeted locus, changes in expression following FCR infection and drought stresses, and the presence of non-synonymous variants between the two isolines, several candidate genes conferring resistance or tolerance to these two types of stresses were identified. The NILs generated, the large number of DEGs with single-nucleotide polymorphisms detected between the two isolines, and the candidate genes identified would be invaluable in fine mapping and cloning the gene(s) underlying the targeted locus.

Barley shows reduced Fusarium head blight under drought and modular expression of differentially expressed genes under combined stress

Plants often face simultaneous abiotic and biotic stress conditions; however, physiological and transcriptional responses under such combined stress conditions are still not fully understood. Spring barley (Hordeum vulgare) is susceptible to Fusarium head blight (FHB), which is strongly affected by weather conditions. We therefore studied the potential influence of drought on FHB severity and plant responses in three varieties of different susceptibility. We found strongly reduced FHB severity in susceptible varieties under drought. The number of differentially expressed genes (DEGs) and strength of transcriptomic regulation reflected the concentrations of physiological stress markers such as abscisic acid or fungal DNA contents. Infection-related gene expression was associated with susceptibility rather than resistance. Weighted gene co-expression network analysis revealed 18 modules of co-expressed genes that reflected the pathogen- or drought-response in the three varieties. A generally infection-related module contained co-expressed genes for defence, programmed cell death, and mycotoxin detoxification, indicating that the diverse genotypes used a similar defence strategy towards FHB, albeit with different degrees of success. Further, DEGs showed co-expression in drought- or genotype-associated modules that correlated with measured phytohormones or the osmolyte proline. The combination of drought stress with infection led to the highest numbers of DEGs and resulted in a modular composition of the single-stress responses rather than a specific transcriptional output.

Improved quantification of Fusarium pseudograminearum (Fusarium crown rot) using qPCR measurement of infection in multi-species winter cereal experiments

Fusarium crown rot (FCR) causes significant grain yield loss in winter cereals around the world. Breeding for resistance and/or tolerance to FCR has been slow with relatively limited success. In this study, multi-species experiments were used to demonstrate an improved method to quantify FCR infection levels at plant maturity using quantitative PCR (qPCR), as well as the genotype yield retention using residual regression deviation. Using qPCR to measure FCR infection allowed a higher degree of resolution between genotypes than traditional visual stem basal browning assessments. The results were consistent across three environments with different levels of disease expression. The improved measure of FCR infection along with genotype yield retention allows for partitioning of both tolerance and partial resistance. Together these methods offer new insights into FCR partial resistance and its relative importance to tolerance in bread wheat and barley. This new approach offers a more robust, unbiased way to select for both FCR traits within breeding programs. Key message: Genetic gain for tolerance and partial resistance against Fusarium crown rot (FCR) in winter cereals has been impeded by laborious and variable visual measures of infection severity. This paper presents results of an improved method to quantify FCR infection that are strongly correlated to yield loss and reveal previously unrecognised partial resistance in barley and wheat varieties.