Metabolomic, Ionomic and Microbial Characterization of Olive Xylem Sap Reveals Differences According to Plant Age and Genotype

Round 1

Reviewer 1 Report

The authors addresses all my previous critiques and suggests.

Reviewer 2 Report

Reviewing of Manuscript Number: agronomy-1253045

 

 

Title: Metabolomic, ionomic and microbial characterization of olive xylem sap reveals differences according to plant age and genotype

 

Summary: the proposed article deals with the chemical and microbial composition of olive xylem sap of adult trees and plantlets. They performed metabolomics analyses by proton NMR and ionome analyses by ICP-OES and characterized the microbial pattern. They realized some statistical analyses to highlight metabolites and element significant to age and/or genotype in correlation with microbial profile.

 

 

Broad comments:

I appreciate that the authors have taken into consideration my various comments.

The addition of microbiological analyzes in the manuscript is a real added value for the promotion of their work.

 

 

Specific comments:

 

• Line 342: paragraph numbering to correct

 

 

 

Decision: I accept this article for publication.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Tha manuscript " Metabolomic characterization of olive xylem sap reveals differences according to plant age and genotype"  use metabolomic and
ionomic approach to abtain a xylem sap composition during development and between genotypes in adult trees. 
The paper is written in a correct English form. These findings are relevant because they highlight the importance of dynamic evaluation in omics studies in olive.
The work raises the need to correlate the composition of xylem sap with the effect it can have on pathogen infections based on the genotype and age of the infected plants. 
I believe that the data contained can be an important guide and comparison
for the design of future experiments aimed at the protection and productivity
of olive trees

Reviewer 2 Report

Reviewing of Manuscript Number: agronomy-1154324

 

 

Title: Metabolomic characterization of olive xylem sap reveals differences according to plant age and genotype

 

Summary: the proposed article deals with the chemical composition of olive xylem sap of adult trees and plantlets. They performed metabolomics analyses by proton NMR and ionome analyses by ICP-OES. They realized some statistical analyses to highlight metabolites and element significant to age and/or genotype.

 

 

Broad comments:

The different parts of this manuscript is unbalanced: Introduction is barely longer than the abstract, the discussion part is very short. The title mention the metabolomolic characterization but not ionome analyses.

 

It is a pity that the health of the olive adult trees and plantlets is not assessed. There is probably the presence of bacteria and fungi, especially for adults, which have an impact on the composition of the sap. Elevated mannitol concentrations are generally correlated with the presence of fungi. This is notably discussed in an article which deserves to be cited in the manuscript (https://doi.org/10.1038/s41598-020-80090-x).Other works interested in the effect of pathogens V. dahliae and X. fastidiosa are cited. I think that the authors should discuss the content of these articles and put them against their results to complete discussion part. The authors announce that their work “will lead to a better understanding of the complex nutritional requirements of olive xylem-inhabiting microorganisms, including its vascular pathogens, and would allow the design of artificial growing media to improve culturing the olive microbiome. But after I finished the manuscript reading, I am not at all convinced that the authors have met their purpose.  They must review the purpose and / or arguments of the discussion. But what would be most interesting is to determine the microbiological profile of the different samples and to make a correlation between endophyte profile and sap composition if some samples show a larger endophyte population. 

 

Specific comments:

 

Materials and Methods

 

• Line 166 : What is the detection mode for ion chromatography? Is it coupled to ICP-OES?
• Line 176: concerning statistical analyses, the authors precise that they performed a log transformation but do not indicate a scaling operation. Did they perform a scaling of their data? And what type (mean, Pareto,…)?
• Line177: the authors could mention the results of Shapiro-wilks and Levene’s tests to justify the use of ANOVA?

 

Results

• What is the pH avec xylem sap? This point is important in NMR since the acido-basic form of a molecule do not have the same chemical shifts. Is it for this reason that the chemical forms of the metabolites are not homogeneous in the manuscript? (acetate/aspartate … but formic/ fumaric acid)
• Paragraph 3.2.: the authors do not cite maleic acid which present p < 0.05

-        Do the authors have an explanation for the variation in ethanol content? Ethanol appear significant for age and age*genotype but standard deviation is very high, as for methanol.

• Line 282: anion F- is not discussed but the content is significant for age.

 

 

Decision: I reject this article for publication.

Comments for author File: Comments.pdf

Reviewer 3 Report

In this manuscript, Anguita-Maeso et al studied metabolic profiles of xylem sap in two olive genotypes at two different stages of growth. They used branches from plantlets and adult olive trees of cultivars ‘Picual’ and ‘Arbequina’ to characterize the chemical composition of xylem sap, that was extracted using a Scholander pressure chamber. While doing so, they used NMR and ICP-OES based approaches. As expected, metabolomic profiles varied when they compared olive plant age and genotype. Further they report that glucose, fructose, sucrose and mannitol, choline, B and PO were  significantly higher in adult trees than in the plantlets among both the olive genotypes.

This is a nicely written manuscript, however there are some concerns that needs to be addressed, before I may recommend it for publication. 

 

Here are some specific comments- 

1. What is the effect of plant age on disease development by soil-borne fungus Verticillium dahliae and the bacterium Xylella  fastidiosa. Is there a direct co-relation to disease or resistance to disease with plant sap composition at different plant age. Please mention

2. Figure 1 legends are too spoty and it is difficult to interpret the data just by reading it. For example, it is not clear to which genotype and what stage olive plants are used. Kindly elaborate on this.

3. Figure 2, depicts hierarchical clustering and heatmap of metabolomic and ionomic profile of xylem sap of adult trees (AD) and plantlets (SD) of ‘Picual’ and ‘Arbequina’ olive cultivars in 8 different samples. To my taste this figure appears crowded. A simplified figure with 2 cultivars, two growth stages and fewer metabolites may appear more visually appealing to the MDPI-Agronomy readers.

4. Another major shortcoming of this analysis is use of only two cultivars and very few sample points. But this may be a basis of future studies.

5. Soil composition can be huge factor in determining The platelets and the adults were grown on different soil types. Authors need to comment as how this might change the sap composition in future studies

 

Reviewer 4 Report

This study focuses on the xylem of Olive trees to determine the metabolites and see if there are difference in xylem based on age and genotype. There were differences found between one and 10-year old plants. Since these plants were collected from different locations, I would suggest more work be completed with plants grown in the same locations to verify the difference that were observed were based on the age and not the growing conditions.

Line 65: remove "nowadays"

Line 145: combine this paragraph with previous one sentence in Section 2.3

Line 189: States a total of 30 metabolites were identify.  Please add how this compares to other trees in the discussion

3. Results.  You collected sap. Did you evaluate the microbiome?  Since you mention this in the paper, why not include the natural flora of the plant.

3. Results. Did you evaluate the amount of micro-plastics found in the xylem.  That could effect the plant a well as well as the metabolite compositions