Gene expression analysis of rocket salad under pre-harvest and postharvest stresses: A transcriptomic resource for Diplotaxis tenuifolia

Abstract

Diplotaxis tenuifolia L. is of important economic value in the fresh-cut industry for its nutraceutical and sensorial properties. However, information on the molecular mechanisms conferring tolerance of harvested leaves to pre- and postharvest stresses during processing and shelf-life have never been investigated. Here, we provide the first transcriptomic resource of rocket by de novo RNA sequencing assembly, functional annotation and stress-induced expression analysis of 33874 transcripts. Transcriptomic changes in leaves subjected to commercially-relevant pre-harvest (salinity, heat and nitrogen starvation) and postharvest stresses (cold, dehydration, dark, wounding) known to affect quality and shelf-life were analysed 24h after stress treatment, a timing relevant to subsequent processing of salad leaves. Transcription factors and genes involved in plant growth regulator signaling, autophagy, senescence and glucosinolate metabolism were the most affected by the stresses. Hundreds of genes with unknown function but uniquely expressed under stress were identified, providing candidates to investigate stress responses in rocket. Dehydration and wounding had the greatest effect on the transcriptome and different stresses elicited changes in the expression of genes related to overlapping groups of hormones. These data will allow development of approaches targeted at improving stress tolerance, quality and shelf-life of rocket with direct applications in the fresh-cut industries.

Short-Term Post-Harvest Stress that Affects Profiles of Volatile Organic Compounds and Gene Expression in Rocket Salad during Early Post-Harvest Senescence

“…Changes in gene expression were detected both during the 24 h stress period in response to the stress treatments, and also persisted after seven days of post-harvest storage. Transcriptomic data indicated that DtTMT was upregulated by all three stresses after 24 h [19,40]. Data here are in agreement but also indicate that the upregulation occurs much earlier, after only 2 to 6 h in the three stresses imposed as compared with the unstressed control.…”

“…Glucosinolates are significantly reduced in rocket leaves after one or two weeks of storage at 4 • C [18]. However, transcriptomic analysis showed that DtTMT expression was upregulated by wounding, as well as cold and ambient dark stresses applied to leaves of Diplotaxis tenuifolia for 24 h following harvest [19]. This presumably increases the breakdown of glucosinolates into isothiocyanates on consumption.…”

“…NAC family transcription factors have a major role in responses to abiotic stress and senescence, because the expression of more than 20 of them increases during stress and senescence [28]. Nine NAC transcription factors were upregulated following exposure of Diplotaxis tenuifolia rocket leaves to a 24 h stress treatment immediately after harvest, including homologues of Arabidopsis thaliana ANAC19 and ANAC59 [19]. Both of these rocket NAC genes were upregulated in response to dehydration, wounding, dark, cold, and salinity.…”

ROS and MAPK Cascades in the Post-harvest Senescence of Horticultural Products

“…Plant senescence is affected by respiratory metabolism, which provides the energy for a range of biochemical processes [9]. In leafy crops such as salads, pre-harvest and post-harvest stresses (even of short duration) contribute to changes in metabolism that accelerate quality losses [10]. The major symptoms of post-harvest senescence of Zizania latifolia are shell etiolation, surface browning, transpiration, respiratory disorders, and tissue hollowness [9].…”

Regulation of the key antioxidant enzymes by developmental processes and environmental stresses in the dark

“…Dark-induced senescence is well characterized by the loss of chlorophyll and proteins, by enhanced ROS production, or by increased lipid peroxidation and membrane permeability. Changes in phytohormones, such as the induction of ethylene (ET) emission and the drop in the content of cytokinins (CKs), are also important regulators of this process, since these two hormones function as the main controllers of senescence (Luschin-Ebengreuth and Zechmann 2016, Cavaiuolo et al 2017). From this aspect, the role of antioxidant enzymes in controlling ROS accumulation is particularly important in darkinduced senescence.…”