A transcriptomic approach highlights induction of secondary metabolism in citrus fruit in response to Penicillium digitatum infection

Abstract

BackgroundPostharvest losses of citrus fruit due to green mold decay, caused by the fungus Penicillium digitaum, have a considerable economic impact. However, little is known about the molecular processes underlying the response of citrus fruit to P. digitatum.ResultsHere we describe the construction of a subtracted cDNA library enriched in citrus genes preferentially expressed in response to pathogen infection followed by cDNA macroarray hybridization to investigate gene expression during the early stages of colonization of the fruit's peel by P. digitatum. Sequence annotation of clones from the subtracted cDNA library revealed that induction of secondary and amino acid metabolisms constitutes the major response of citrus fruits to P. digitatum infection. Macroarray hybridization analysis was conducted with RNA from either control, wounded, ethylene treated or P. digitatum infected fruit. Results indicate an extensive overlap in the response triggered by the three treatments, but also demonstrated specific patterns of gene expression in response to each stimulus. Collectively our data indicate a significant presence of isoprenoid, alkaloid and phenylpropanoid biosynthetic genes in the transcriptomic response of citrus fruits to P. digitatum infection. About half of the genes that are up-regulated in response to pathogen infection are also induced by ethylene, but many examples of ethylene-independent gene regulation were also found. Two notable examples of this regulation pattern are the genes showing homology to a caffeine synthase and a berberine bridge enzyme, two proteins involved in alkaloid biosynthesis, which are among the most induced genes upon P. digitatum infection but are not responsive to ethylene.ConclusionsThis study provided the first global picture of the gene expression changes in citrus fruit in response to P. digitatum infection, emphasizing differences and commonalities with those triggered by wounding or exogenous ethylene treatment. Interpretation of the differentially expressed genes revealed that metabolism is redirected to the synthesis of isoprenes, alkaloids and phenylpropanoids.

Effectiveness of Postharvest Treatment with Chitosan to Control Citrus Green Mold

“…Before reaching the market, harvested fruits are usually stored for fresh consumption. During the postharvest period, fungal disease infection is the leading source of fresh citrus fruit decay [2]. Green mold caused by Penicillium digitatum (Pers.:Fr.)…”

Assessing the Biosynthetic Capabilities of Secretory Glands inCitrusPeel

“…Previous transcriptome studies of Citrus fruit peel and peel sections were designed to investigate stress and defense responses but did not provide direct insights into essential oil biosynthesis (Maul et al, 2008;González-Candelas et al, 2010;Matas et al, 2010;Ballester et al, 2011;Hershkovitz et al, 2012). We optimized a protocol for the collection of intact ECs from the flavedo layer of grapefruit peel by laser microdissection and pressure catapulting, subsequent isolation of RNA, and linear amplification of transcripts for analysis on Affymetrix Citrus genome oligonucleotide microarrays.…”

“…For example, transcripts related to terpenoid synthases, which catalyze the first committed step in the biosynthesis of terpenoid essential oil constituents, were highly expressed in Citrus fruit peel when compared with other tissues and organs Dornelas and Mazzafera, 2007;Takita et al, 2007). More recently, genome-wide oligonucleotide microarray analyses have been conducted with Citrus peel tissue (Maul et al, 2008;González-Candelas et al, 2010;Matas et al, 2010;Ballester et al, 2011;Hershkovitz et al, 2012). However, these studies were aimed at evaluating specific developmental processes or stress/ defense responses of Citrus and did not provide direct insights into peel essential oil biosynthesis.…”

YeATSAM analysis of the walnut and chickpea transcriptome reveals key genes undetected by current annotation tools

“…These enigmatic enzymes are implicated in the transformation of (S)-reticuline to (S)-scoulerine during benzophenanthridine alkaloid biosynthesis in plants ( Winkler et al , 2006). This pathway is over-expressed upon osmotic stress and pathogen attack ( Attila et al , 2008; González-Candelas et al , 2010), provides resistance in lettuce, sunflower and transgenic tobacco by generating anti-microbial compounds ( Custers et al , 2004), and has unknown functions at specific developmental stages in Arabidopsis ( Irshad et al , 2008; Pagnussat et al , 2005). Moreover, it is expressed in floral nectar (Nectarin V, Nt BBE) ( Carter & Thornburg, 2004) and roots of tobacco ( Kajikawa et al , 2011), and in xylem sap of cabbage ( Ligat et al , 2011) and grapevine ( Chakraborty et al , 2016b).…”