Transcriptome Analysis of Mature Fruit Abscission Control in Olive

Abstract

Mature fruit abscission (MFA) is a genetically controlled process, through poorly characterized mechanisms in fleshy fruit that include extensive transcriptional changes. While global transcriptome analyses have been used to investigate immature fruit abscission in fleshy fruit, no global gene expression changes specific to MFA have been described. Here we use pyrosequencing to characterize the transcriptomes of the olive abscission zone (AZ) during cell separation in order to understand MFA control at the stage of AZ activation. Analysis of gene expression from these AZs reveals that membrane microdomains involving sterols/sphingolipids and remorins together with signaling proteins are potentially involved in MFA. This is accompanied by gene activity related to sphingolipid turnover, suggesting potentially the involvement of long-chain base metabolism in regulating MFA. Activation of vesicle trafficking involving small GTPases is probably required for cell wall modifications during abscission. Analysis of transcription factors indicates that most members of the MYB and bZIP families are abundantly represented in the fruit AZ, and is consistent with a model by which most of the key transcription factors during abscission may regulate downstream processes mostly related to ABA. The data provide the first thorough analysis available for a comprehensive picture of the array of cellular responses controlled by gene expression that lead to MFA in fleshy fruit.

Comparative transcriptional profiling analysis of olive ripe-fruit pericarp and abscission zone tissues shows expression differences and distinct patterns of transcriptional regulation

“…Among the most abundant AZ-enriched transcripts, we identified a homolog of STH-2 (Similar to pathogenesis-related protein 2) (Table 1), encoding a pathogenesis-related protein (PR), which are observed in the olive AZ during the induction of mature-fruit abscission [9]. However, further work is necessary to ascertain the biological significance of pathogenesis-related gene expression in the olive AZ during abscission.…”

“…This includes, for example, a beta-1,3-glucanase, which catalyze the hydrolysis of β-1,3-glucan linkages of callose, as well as participating in many processes including cell-wall remodeling, secondary-wall formation, and phytohormone activation [27]. Reportedly, abscission induction is accompanied by the marked up-regulation of a gene that encodes β-1,3-glucanase, as well as the down-regulation of a gene that encodes a callose synthase in the fruit-AZ [9]. This activation of beta-1,3-glucanase was stronger in olive AZ, showing that this phenomenon is related to fruit abscission in olive.…”

“…Also, sequencing of the olive genome has been undertaken in Italy through the project OLEA (http://www.oleagenome.org/). Concomitantly, a number of large datasets of expressed sequence tag (EST) datasets have recently been reported for olive, generating 261,485 ESTs [2] and 443,811 ESTs [9] employing the 454 pyrosequencing technologies, an additional 1,132 ESTs with the use of suppression subtractive hybridization [3], as well as 2 million ESTs using Sanger and 454 pyrosequencing technologies [10], this being important for extending the catalog of olive transcripts in order to facilitate gene discovery, functional analysis, and molecular breeding.…”

“…Picual), fruit ripening associated events lead finally to the abscission of the ripe fruit from the pedicel, this taking place at 217 days post-anthesis (DPA) [14, 15]. In a previous study, we reported the comparison of the Picual fruit AZ transcriptomes at two different stages (pre-abscission vs. abscission) using the RNA-Seq technique; 148 Mb of sequences (443,811 good-quality sequence reads) resulted and 4,728 differentially expressed genes were identified from these two samples [9]. Among the 70 TF genes induced during mature-fruit abscission in the olive AZ, the classes that are well represented included bZIP proteins, MYB proteins, and homeobox domain proteins [9].…”

“…In a previous study, we reported the comparison of the Picual fruit AZ transcriptomes at two different stages (pre-abscission vs. abscission) using the RNA-Seq technique; 148 Mb of sequences (443,811 good-quality sequence reads) resulted and 4,728 differentially expressed genes were identified from these two samples [9]. Among the 70 TF genes induced during mature-fruit abscission in the olive AZ, the classes that are well represented included bZIP proteins, MYB proteins, and homeobox domain proteins [9]. The comparison between AZ and fruit allow us to restrict the set of genes putatively related to the abscission, and in this direction the results may hold worthwhile perspectives for the study of this process.…”