Towards a Cardoon (Cynara cardunculus var. altilis)-Based Biorefinery: A Case Study of Improved Cell Cultures via Genetic Modulation of the Phenylpropanoid Pathway.

Alberto Ritieni,Sara Pozzo,Dario Paolo,Monica De Palma,Raul Pirona,Giulia Graziani,Franca Locatelli,Teresa Docimo,Francesca Sparvoli,Eleonora Cominelli,Marina Tucci

doi:10.3390/ijms222111978

Abstract

Cultivated cardoon (Cynara cardunculus var. altilis L.) is a promising candidate species for the development of plant cell cultures suitable for large-scale biomass production and recovery of nutraceuticals. We set up a protocol for Agrobacterium tumefaciens-mediated transformation, which can be used for the improvement of cardoon cell cultures in a frame of biorefinery. As high lignin content determines lower saccharification yields for the biomass, we opted for a biotechnological approach, with the purpose of reducing lignin content; we generated transgenic lines overexpressing the Arabidopsis thaliana MYB4 transcription factor, a known repressor of lignin/flavonoid biosynthesis. Here, we report a comprehensive characterization, including metabolic and transcriptomic analyses of AtMYB4 overexpression cardoon lines, in comparison to wild type, underlining favorable traits for their use in biorefinery. Among these, the improved accessibility of the lignocellulosic biomass to degrading enzymes due to depletion of lignin content, the unexpected increased growth rates, and the valuable nutraceutical profiles, in particular for hydroxycinnamic/caffeoylquinic and fatty acids profiles.

Highlights

Among the family of Asteraceae, Cynara cardunculus L. (2n = 2x = 34) is a species of perennial herbaceous plants with annual growth cycle; the species consists of three closely related botanical varieties: the wild cardoon, the globe artichoke, and the cultivated cardoon [1]
Relative differences of FW observed between wild type (WT) and AtMYB4oe lines were confirmed in the comparison of dry weights (DW), as the percentage of the ratio between DW and FW was nearly identical for all samples (3.6%)
We showed that lignin content was severely reduced in AtMYB4oe lines, and the depletion of total phenols and lignin was reflected by the RNA-seq data: Gene Ontology Enrichment Analysis (GOEA) of differentially expressed genes (DEGs) revealed the downregulation of genes involved in phenylpropanoid biosynthesis and, in lignin biosynthesis and cell wall organization

Summary

Introduction

(2n = 2x = 34) is a species of perennial herbaceous plants with annual growth cycle; the species consists of three closely related botanical varieties: the wild cardoon Given the full cross-compatibility between these varieties, in addition to phenotypic and genetic evidences, previous studies concluded that both the cultivated cardoon and the globe artichoke were domesticated from wild cardoons [2,3]. Cultivated cardoons are well-adapted to the semi-arid environment of the Mediterranean basin, where they are considered a traditional crop. Over the last 30 years, the potential of cultivated cardoon for biomass production has been increasingly investigated [5,6]. Cardoon is a highly adaptive species able to tolerate abiotic stresses such as soil salinity [8,9], drought [10], and soil contamination by heavy metals [11,12]

Methods

Results

Conclusion