Transcriptome Analyses Shed New Insights into Primary Metabolism and Regulation of Blumeria graminis f. sp. tritici during Conidiation

Abstract

Conidia of the obligate biotrophic fungal pathogen Blumeria graminis f. sp. tritici (Bgt) play a vital role in its survival and rapid dispersal. However, little is known about the genetic basis for its asexual reproduction. To uncover the primary metabolic and regulatory events during conidiation, we sequenced the transcriptome of Bgt epiphytic structures at 3 (vegetative hyphae growth), 4 (foot cells initiation), and 5 (conidiophore erection) days post-inoculation (dpi). RNA-seq analyses identified 556 and 404 (combined 685) differentially expressed genes (DEGs) at 4 and 5 dpi compared with their expression levels at 3 dpi, respectively. We found that several genes involved in the conversion from a variety of sugars to glucose, glycolysis, the tricarboxylic acid cycle (TAC), the electron transport chain (ETC), and unsaturated fatty acid oxidation were activated during conidiation, suggesting that more energy supply is required during this process. Moreover, we found that glucose was converted into glycogen, which was accumulated in developing conidiophores, indicating that it could be the primary energy storage molecule in Bgt conidia. Clustering for the expression profiles of 91 regulatory genes showed that calcium (Ca 2+ ), H 2 O 2 , and phosphoinositide (PIP) signaling were involved in Bgt conidiation. Furthermore, a strong accumulation of H 2 O 2 in developing conidiophores was detected. Application of EGTA, a Ca 2+ chelator, and trifluoperazine dihydrochloride (TFP), a calmodulin (CaM) antagonist, markedly suppressed the generation of H 2 O 2 , affected foot cell and conidiophore development and reduced conidia production significantly. These results suggest that Ca 2+ and H 2 O 2 signaling play important roles in conidiogenesis and a crosslink between them is present. In addition to some conidiation-related orthologs known in other fungi, such as the velvet complex components, we identified several other novel B. graminis-specific genes that have not been previously found to be implicated in fungal conidiation, reflecting a unique molecular mechanism underlying asexual development of cereal powdery mildews.

The Biotrophic Development of Ustilago maydis Studied by RNA-Seq Analysis

“…tritici and P. striiformis f. sp. tritici effector expression waves have also been described (Hacquard et al, 2013;Dobon et al, 2016;Zeng et al, 2017), reinforcing the idea that the need for certain effectors changes during host colonization and that this is a conserved feature of different pathosystems.…”

“…To promote the respective colonization strategy pathogens secrete a large arsenal of effector proteins. In recent years the study of lifestyle transitions in plant pathogenic fungi by time resolved transcriptome analyses through RNAseq provided deep insights into the processes associated with stages of fungal development on and inside the host (Kawahara et al, 2012;O'Connell et al, 2012;Hacquard et al, 2013;Jupe et al, 2013;Dong et al, 2015;Fondevilla et al, 2015;Kong et al, 2015;Rudd et al, 2015;Dobon et al, 2016;Thatcher et al, 2016;Copley et al, 2017;Wang et al, 2017;Zeng et al, 2017;Massonnet et al, 2018). These and other studies (Toruno et al, 2016) have shown that different sets of effectors are synthesized and presumably needed during discrete developmental stages in fungal pathogens.…”

Comparative transcriptome profiling of Blumeria graminis f. sp. tritici during compatible and incompatible interactions with sister wheat lines carrying and lacking Pm40

“…Although several studies have investigated powdery mildew pathogens in both barley and Arabidopsis [ 33 , 34 , 24 , 20 ], fewer studies have investigated the Bgt pathogen in wheat [ 15 , 38 ]. In present study, the different transcript expression patterns of Bgt during compatible and incompatible interactions and the relationships with fungal morphological growth have been determined.…”

“…In a recent study, the transcriptome of Bgt showed that activation of the metabolism of diverse sugars, glycogen synthesis, energy production, and unsaturated fatty acid oxidation occurred during Bgt conidiation. A crosslink between H 2 O 2 and Ca 2+ signaling and involvement of some other regulators are associated with regulation of Bgt conidiation [ 38 ]. Proteomic studies of Bgh have focused on purified haustoria, haustoria in barley epidermis, conidia and secondary hyphae, and most proteins appear to be involved in metabolic pathways or biological energy production [ 39 – 42 ].…”

Protein type and lifestyle contribute to the evolution of low complexity regions in proteins of plant colonizing fungi

“…Moreover, effectors were found to localize and function in different plant cellular compartments [59]. Effectors were also shown to be expressed in a colonization-stage dependent manner, that is, some effectors are already expressed when the fungus grows on the plant surface, whereas others are expressed only during late infection stages [60][61][62][63][64]. Such data are not yet available for a larger number of pathosystems, which makes it difficult to integrate them in current comparative studies.…”