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The salicylic acid receptor NPR1 (nonexpressor of pathogenesis-related genes) and its paralogues NPR3 and NPR4 are master regulators of plant immunity. Commercial strawberry (Fragaria × ananassa) is a highly valued crop vulnerable to various pathogens. Historic confusions regarding the identity of NPR-like genes have hindered research in strawberry resistance. In this study, the comprehensive identification and phylogenic analysis unraveled this family, harboring 6, 6, 5, and 23 members in F. vesca, F. viridis, F. iinumae, and F. × ananassa, respectively. These genes were clustered into three clades, with each diploid member matching three to five homoalleles in F. × ananassa. Despite the high conservation in terms of gene structure, protein module, and functional residues/motifs/domains, substantial divergence was observed, hinting strawberry NPR proteins probably function in ways somewhat different from Arabidopsis. RT-PCR and RNAseq analysis evidenced the transcriptional responses of FveNPR1 and FxaNPR1a to Colletotrichum fructicola. Extended expression analysis for strawberry NPR-likes helped to us understand how strawberry orchestrate the NPRs-centered defense system against C. fructicola. The cThe current work supports that FveNPR1 and FxaNPR1a, as well as FveNPR31 and FxaNPR31a-c, were putative functional orthologues of AtNPR1 and AtNPR3/4, respectively. These findings set a solid basis for the molecular dissection of biological functions of strawberry NPR-like genes for improving disease resistance. [ABSTRACT FROM AUTHOR]

Anthracnose, a destructive disease in strawberry worldwide, is caused by the pathogenic fungus Colletotrichum ssp.. To date, numerous studies focusing on its identification, pathogenicity and biological characteristics have been published. However, research on quantifying the colonization of this pathogen is still lacking, which is crucial to the study of anthracnose resistance. In this study, we developed a sensitive primer pair targeting the cutinase gene that is capable of distinguishing Colletotrichum gloeosporioides (C. gloeosporioides) species complex, the main species causing strawberry anthracnose in China, including C. fructicola, C. gloeosporioides, C. aenigma and C. siamense, from other Colletotrichum species and typical fungal pathogens. On this basis, we established a quantitative real‐time PCR (qRT‐PCR) assay to accurately quantify pathogen amounts from both pure cultures and infected strawberries, with detection limits of 105–101 copies. Using this method, we characterized quantitative traits of C. fructicola colonization in strawberry leaves and discovered differences in pathogen populations at different positions. Moreover, monitoring of pathogen growth during infection showed a dynamic change in the amount of C. fructicola. Finally, a comparison of the absolute and relative quantification results further proved this method's validity. Therefore, we propose that this specific PCR method enables rapid detection and quantification of C. gloeosporioides species complex colonization in strawberry and will be a useful tool for anthracnose management and strawberry resistance studies. [ABSTRACT FROM AUTHOR]

BACKGROUND: Strawberry fruits are perishable with a short post-harvest life. Cinnamyl alcohol dehydrogenase (CAD) is the key enzyme for lignin biosynthesis strengthening plant cell wall. A systematic characterization of strawberry CAD family is absent and their involvement in fruit firmness is largely elusive. OBJECTIVE: Current work aims for a genome-wide identificationof CAD family and its expression correlation with fruit firmness in strawberry varieties. METHODS: A genome-scale identification and molecular characterization for CADs were performed in the commercial strawberry (Fragaria×ananassa) and woodland strawberry (F. vesca). qPCR analysis of CAD homoeologs in three cultivars varying with fruit firmness revealed candidate CAD members positively correlated with lignin content and fruit firmness. RESULTS: A total of 14 and 24 CAD loci were identified in the genomes of F.vesca var. Hawaii4 and F. ×ananassa cv. Camarosa, respectively.Phylogenetic analysis supported a division of this family into three classes. Class I FvCAD each has four homoeologs in commercial strawberry, while those of Class II and Class III have only one or two homoeologs. Except for FvCAD2 and -6, there exits at least one pair of CADs sharing ∼97% or above amino acid identity between F. vesca and F. ×ananassa.The flesh firmness and lignin content varied greatly among strawberry germplasm. Distinct dynamic changes in fruit lignin content were observed before the large green stage, but fruit firmness displayed a similar decrease profile during fruit development in three varieties. Of the eight genes detected in F.×ananassa, FvCAD3 and -12 did not display a F. vesca-biased expression pattern during fruit development.FvCAD4 of Class I was expressed at levels positively correlated with variation in fruit lignin content at white stage.Transcript abundance of five Class IIgenes including FvCAD3, -8, -10, -11, and -12 was positively correlated with lignin content and fruit firmness, with FvCAD10 and -11 (FaCAD in previous publication) reaching an extremely significant correlation with the genetic variation in fruit firmness across three varieties. CONCLUSION: Strawberry Class II CADs were significantly correlated with the genetic variation in fruit firmness, which might expand the potential choices for improving strawberry shelf life. [ABSTRACT FROM AUTHOR]

Colletotrichum fructicola, which is part of the C. gloeosporioides species complex, can cause anthracnose diseases in strawberries worldwide. However, the molecular interactions between C. fructicola and strawberry are largely unknown. A deep RNA-sequencing approach was applied to gain insights into the pathogenicity mechanisms of C. fructicola and the defense response of strawberry plants at different stages of infection. The transcriptome data showed stage-specific transcription accompanied by a step-by-step strawberry defense response and the evasion of this defense system by fungus. Fungal genes involved in plant cell wall degradation, secondary metabolism, and detoxification were up-regulated at different stage of infection. Most importantly, C. fructicola infection was accompanied by a large number of highly expressed effectors. Four new identified effectors function in the suppression of Bax-mediated programmed cell death. Strawberry utilizes pathogen-associated molecular patterns (PAMP)-triggered immunity and effector-triggered immunity to prevent C. fructicola invasion, followed by the initiation of downstream innate immunity. The up-regulation of genes related to salicylic acid provided evidence that salicylic acid signaling may serve as the core defense signaling mechanism, while jasmonic acid and ethylene pathways were largely inhibited by C. fructicola. The necrotrophic stage displayed a significant up-regulation of genes involved in reactive oxygen species activation. Collectively, the transcriptomic data of both C. fructicola and strawberry shows that even though plants build a multilayered defense against infection, C. fructicola employs a series of escape or antagonizing mechanisms to successfully infect host cells. [ABSTRACT FROM AUTHOR]