Tissue-specific signatures of metabolites and proteins in asparagus roots and exudates

Abstract

Comprehensive untargeted and targeted analysis of root exudate composition has advanced our understanding of rhizosphere processes. However, little is known about exudate spatial distribution and regulation. We studied the specific metabolite signatures of asparagus root exudates, root outer (epidermis and exodermis), and root inner tissues (cortex and vasculature). The greatest differences were found between exudates and root tissues. In total, 263 non-redundant metabolites were identified as significantly differentially abundant between the three root fractions, with the majority being enriched in the root exudate and/or outer tissue and annotated as ‘lipids and lipid-like molecules’ or ‘phenylpropanoids and polyketides’. Spatial distribution was verified for three selected compounds using MALDI-TOF mass spectrometry imaging. Tissue-specific proteome analysis related root tissue-specific metabolite distributions and rhizodeposition with underlying biosynthetic pathways and transport mechanisms. The proteomes of root outer and inner tissues were spatially very distinct, in agreement with the fundamental differences between their functions and structures. According to KEGG pathway analysis, the outer tissue proteome was characterized by a high abundance of proteins related to ‘lipid metabolism’, ‘biosynthesis of other secondary metabolites’ and ‘transport and catabolism’, reflecting its main functions of providing a hydrophobic barrier, secreting secondary metabolites, and mediating water and nutrient uptake. Proteins more abundant in the inner tissue related to ‘transcription’, ‘translation’ and ‘folding, sorting and degradation’, in accord with the high activity of cortical and vasculature cell layers in growth- and development-related processes. In summary, asparagus root fractions accumulate specific metabolites. This expands our knowledge of tissue-specific plant cell function.

Metabolomics Reveals Heterogeneity in the Chemical Composition of Green and White Spears of Asparagus (A. officinalis)

“…This differentiation of the profiles in flavonoids (more abundant in green) and saponins (more abundant in white spears) might have been anticipated since previous studies have reported generally high flavonoid contents in photosynthetic tissues [ 40 ], and high saponin levels in plant parts growing below-ground [ 18 , 38 ]. Using a complementary approach, Yi et al, (2019) performed de novo transcriptome sequencing in both green and white types of a commercial variety (Atlas) and found significant differences between the two asparagus types in that 21% of the genes involved in the biosynthesis of the flavonoid rutin were upregulated in green and 4% of the genes involved in the biosynthesis of the saponin protodioscin were upregulated in white asparagus [ 41 ].…”

Effect of Salt Stress on Growth and Physiological Properties of Asparagus Seedlings

“…Asparagus ( Asparagus officinalis L.) belongs to the lily family, is a perennial and diecious vegetable popularly consumed worldwide. Asparagus contains a high level of nutrients and antioxidant compounds, and has positive effects on preventing hypertension, heart disease and certain cancers [ 27 , 28 , 29 ]. Asparagus originate in the Mediterranean region andis now cultivatedin many countries worldwide.…”

The use of ecological analytical tools as an unconventional approach for untargeted metabolomics data analysis: the case of Cecropia obtusifolia and its adaptive responses to nitrate starvation

“…Using leaf and stem segments, different metabolites of each species were identified depending on the analyzed organ segment, and it was concluded that the elaboration of metabolomic profiles is a useful tool aiding the rapid characterization of metabolites in plants and, thus, revealing their chemodiversity (diversity of phytochemicals delimited according to botanical taxa and/or tissues or specific phenological states) (Lee et al 2020 ; Müller et al 2020 ; Saito 2020 ). Similarly, there are many valuable studies in which high-performance metabolomic tools are used to investigate the metabolic diversity to evaluate plant diversity (Döll et al 2021 ; Marr et al 2021 ). However, most of these studies adopt the analysis of chemodiversity as a useful approach solely for comparisons between different conditions (experimental variables), without truly evaluating diversity and/or structural patterns based on a strict census of the phytochemical compounds that make up the metabolome per se (Shi et al 2020 ; Zhao et al 2020 ).…”