Identification and Functional Annotation of Genes Differentially Expressed in the Reproductive Tissues of the Olive Tree (Olea europaea L.) through the Generation of Subtractive Libraries

Abstract

The olive tree is a crop of high socio-economical importance in the Mediterranean area. Sexual reproduction in this plant is an essential process, which determines the yield. Successful fertilization is mainly favored and sometimes needed of the presence of pollen grains from a different cultivar as the olive seizes a self-incompatibility system allegedly determined of the sporophytic type. The purpose of the present study was to identify key gene products involved in the function of olive pollen and pistil, in order to help elucidate the events and signaling processes, which happen during the courtship, pollen grain germination, and fertilization in olive. The use of subtractive SSH libraries constructed using, on the one hand one specific stage of the pistil development with germinating pollen grains, and on the other hand mature pollen grains may help to reveal the specific transcripts involved in the cited events. Such libraries have also been created by subtracting vegetative mRNAs (from leaves), in order to identify reproductive sequences only. A variety of transcripts have been identified in the mature pollen grains and in the pistil at the receptive stage. Among them, those related to defense, transport and oxidative metabolism are highlighted mainly in the pistil libraries where transcripts related to stress, and response to biotic and abiotic stimulus have a prominent position. Extensive lists containing information as regard to the specific transcripts determined for each stage and tissue are provided, as well as functional classifications of these gene products. Such lists were faced up to two recent datasets obtained in olive after transcriptomic and genomic approaches. The sequences and the differential expression level of the SSH-transcripts identified here, highly matched the transcriptomic information. Moreover, the unique presence of a representative number of these transcripts has been validated by means of qPCR approaches. The construction of SSH libraries using pistil and pollen, considering the high interaction between male-female counterparts, allowed the identification of transcripts with important roles in stigma physiology. The functions of many of the transcripts obtained are intimately related, and most of them are of pivotal importance in defense, pollen-stigma interaction and signaling.

Genome wide association study of 5 agronomic traits in olive (Olea europaea L.)

“…This gene is annotated as a PHD finger transcription factor and the family to which this gene belongs, plays a key role in regulating plant growth and development 86 . The analysis of transcriptomes provides genomic resources for functional annotation to discover genes for olive breeding 87 . To date, several transcriptome studies have been performed for olive using different organs at different developmental stages 41,47,87–89 .…”

“…The analysis of transcriptomes provides genomic resources for functional annotation to discover genes for olive breeding 87 . To date, several transcriptome studies have been performed for olive using different organs at different developmental stages 41,47,87–89 . There have been attempts to identify candidate genes associated with important traits such as plant architecture 90 and juvenility 91 in olive, but no putative candidate genes underlying QTL have been reported.…”

How to Choose a Good Marker to Analyze the Olive Germplasm (Olea europaea L.) and Derived Products

“…Again, the advent of next-generation sequencing (NGS) greatly enhanced transcriptome analysis, making it, in just a few years, a powerful method for rapidly identifying molecular markers associated with trait variation, leveraging both variations of the gene sequence and the variation of gene expression [175]. In particular, the use of RNA-seq was further consolidated by the lower cost per base pair, short time requirement and lack of subcloning process [176], becoming the preferred approach for transcriptomic studies in olive tree organs development [166,[177][178][179], but especially for studying olive responses to biotic and abiotic stresses. Differential gene expression in relation to fruit total fatty acid content variations (palmitic, oleic and linoleic acid) was studied under adverse environmental conditions such as cold [180], salt stress [181,182], drought [183].…”

Unraveling salt‐responsive tissue‐specific metabolic pathways in olive tree

“…It must be pointed out also that the saline stress on mature leaves can affect the development of new leaves (Benjamin et al 2019). Recently, the transcriptomic analysis of various olive tissues revealed a complex dynamic pattern of gene expression in each tissue in response to stress conditions (Jiménez-Ruiz et al 2017;Zafra et al 2017;Ramírez-Tejero et al 2020;Skodra et al 2021). This hinted at the existence of distinct regulatory programs associated with specialized tissue responses.…”