Role of Non-Structural Sugar Metabolism in Regulating Tuber Dormancy in White Yam (Dioscorea rotundata)

Round 1

Reviewer 1 Report

1. Abstract, line 26, indicate that TDr1100873 is an improved genotype as you have done for the local variety.

2. results, line 284, "was gradual decrease in total sugar from DAPM to 101DAPM''.  indicate the specific DAPM

3. Figure 7. a & b present the same information, why not just use one?? 

4. Discussions, line 439, "6DAPM", I guess you meant to write 56 DAPM

5. line 479, replace "Pls cite here" with the proper citation.

6. Table 1, Define the abbreviation TDrObia at the footnote.

Also check lines 500, 493, 420 and 418 to correct minor typo errors

Author Response

My Responses to the First Round Reviewers Comments

On behalf of the co-authors of the manuscript with the above-mentioned ID I wish to present the following responses to the reviewers’ comments.

 

I want to sincerely appreciate the efforts of the reviewers towards ensuring that this manuscript comes out in its possible best form. Indeed, their comments and inputs have help in reshaping and fine-tuning the manuscript.

 

Reviewer 1 comments

Abstract; 1. Abstract, line 26, indicate that TDr1100873 is an improved genotype as you have done for the local variety

Response: The suggestion to indicate TDr1100873 as improve genotype was taken and correction was done.

Results

2. results, line 284, "was gradual decrease in total sugar from DAPM to 101DAPM''.  indicate the specific DAPM
3. Figure 7. a & b present the same information, why not just use one?? 
4. Discussions, line 439, "6DAPM", I guess you meant to write 56 DAPM
5. line 479, replace "Pls cite here" with the proper citation.
6. Table 1, Define the abbreviation TDrObia at the footnote.

Also check lines 500, 493, 420 and 418 to correct minor typo errors

Responses

The errors observed in lines 284, 418, 439, 420, 439 and 500 have been corrected

Appropriate citation was inserted at line 479 as suggested

Footnote has been added at the foot of table 1 describing TDrObia

Figure 7a and b; we quite agree with the reviewer that the two figures are presenting the same result, however, we wish to appeal that the two figures should be allowed, because each of the figure added value and improved the clarity of the result. For instance, while figure 7a showed correlation matrix box between the parameters investigated with correlations coefficient (r)values attached as legend beside the box, Figure 7b showed the correlations between the parameters in a node and edge network format. 

Reviewer 2 Report

In this work authors compare two yam genotypes, Obiaturuga and TDrr1100873 differing in their dormancy before sprouting. While Obiaturuga has a comparably short dormancy phase, the dormancy of TDrr1100873 takes 40 days longer. The research is in general interesting and additional value is generated by investigating the important but largely neglected crop yam.

However, I find the paper difficult to read and the presented figures unfinished. This is especially true for the crowded Fig. 2, where individual kinetics of sugars and parameters are very hard to read. I think, the focus before publication should be to revise the figures, enhance their readability and resolution and to accurately describe figure content in the legends.

In addition, there are more specific issues, which the authors might address:

Title: The term “non-structural sugar metabolism” is unclear. At least to my knowledge sugars are all considered non-structural.

Affiliations: There is no author who is affiliated with #6 (University of Würzburg)

 

Introduction:

L42f: The statement “Yam [has] better organoleptic properties compared to cassava, potato and sweet potato seems a bit subjective and is probably dependent on the genotype of the crops mentioned

L63: The sentence “The regulatory roles of sugar are most explicit in a free-living microorganism that are often challenged by the constant changing 64 environment.” It is unclear which microorganisms do the authors have in mind?

 Results:

Figure 1: I don’t understand how the sprouting analysis of the two genotypes was conducted? In the material and methods section authors report that tubers were sampled at e.g. 101 or 143 days. How was the end of the dormancy recorded and how many tubers were used for the analysis? This information should be included in the text. Moreover, the significance of difference between the two genotypes should be denoted by asterisks.

Figure 2: The “Values” on the Y-axes are unclear. What is depicted here? Also please be aware that the error bars do not denote significant differences! Which statistical test has been used to assess the significance? You also need to write how many replicates have been used per data point.

 Discussion:

The discussion is sometimes highly exaggerated in terms of putative regulation of sugars, trehalose-6-phosphate, SNRK1 activity and dormancy breaking (from L. 505 onwards). Without measuring the involved metabolites and gene expression the involved statements cannot be made. I suggest that the authors stick to the discussion of the results presented. In this regard it should be discussed, whether the observed increase of monosaccharides at dormancy breaking/bud emergence might be rather the sole consequence of re-mobilization of starch due to increased sink strength of the newly formed tuber buds.

Author Response

Reviewer 2

Comment 1; In this work authors compare two yam genotypes, Obiaturuga and TDrr1100873 differing in their dormancy before sprouting. While Obiaturuga has a comparably short dormancy phase, the dormancy of TDrr1100873 takes 40 days longer. The research is in general interesting and additional value is generated by investigating the important but largely neglected crop yam.

Response; This positive comment was appreciated but, we want to state that the objective of the study was not to compare the two genotypes, instead we compared the non-structural sugar metabolism from dormancy to sprouting in the tubers of the two genotypes, but along the line we found that there was variation between the two genotypes with respect to the tuber dormancy duration between the two genotypes.

Comment 2; However, I find the paper difficult to read and the presented figures unfinished. This is especially true for the crowded Fig. 2, where individual kinetics of sugars and parameters are very hard to read. I think, the focus before publication should be to revise the figures, enhance their readability and resolution and to accurately describe figure content in the legends.

Responses; The resolution been increased to the maximum 300dpi and more information has been added to footnote sufficiently describing the figure. The rest of figures we think are clear enough with sufficient legends describing them.

Comment 3; Title: The term “non-structural sugar metabolism” is unclear. At least to my knowledge sugars are all considered non-structural.

Response; Non-structural sugars are storable sugars in the plant cell, excluding the sugars (mostly oligosaccharides) in the cell wall. The non-structural sugars are the sugars that play roles in plant physiological activities, whereas, structural sugars provide structural or frame support to the cell, and methods of extracting these two group sugars differs. Hence, our study we focused on non-structural sugars, and we have extracted and analyzed only non-structural sugars.

Comment 4: Affiliations: There is no author who is affiliated with #6 (University of Würzburg)

Response; Dr Cynthia A. Chilaka is from the University  of Würzburg; it was an error and it has been corrected.

 

 

Introduction:

Comment 5; L42f: The statement “Yam [has] better organoleptic properties compared to cassava, potato and sweet potato seems a bit subjective and is probably dependent on the genotype of the crops mentioned

L63: The sentence “The regulatory roles of sugar are most explicit in a free-living microorganism that are often challenged by the constant changing 64 environment.” It is unclear which microorganisms do the authors have in mind?

Response; These information were extract from already published articles, which were cited in our manuscripts.

Results:

Comment 6; Figure 1: I don’t understand how the sprouting analysis of the two genotypes was conducted? In the material and methods section authors report that tubers were sampled at e.g. 101 or 143 days. How was the end of the dormancy recorded and how many tubers were used for the analysis? This information should be included in the text. Moreover, the significance of difference between the two genotypes should be denoted by asterisks.

Response; First, we did not report that tubers were sampled at 101 or 143 days in the material and methods. We stated that tubers were sampled from 42 days after physiological maturity (DAPM) to dormancy break point (101 DAPM) for Obiaoturugo (short dormant) genotype; at 42 DAPM, 56 DAPM, 87 DAPM and 101 DAPM. Whereas, for TDr1100873 (long dormant) genotype; tubers were sampled from 42 DAPM to dormancy break point (143 DAPM) at; 42 DAPM, 56 DAPM, 87 DAPM, 101 DAPM, 143 DAPM. This was how determined dormancy end, and these were all included in the materials and method. Difference in dormancy duration between the two genotypes was determined by performing simple t. test and significance difference between the two genotypes have been denoted with asterisks at the footnote.     

Comment 7; Figure 2: The “Values” on the Y-axes are unclear. What is depicted here? Also please be aware that the error bars do not denote significant differences! Which statistical test has been used to assess the significance? You also need to write how many replicates have been used per data point.

Response; Figure 2 a and b showed the overview of the performance of the whole sugar parameters, dry matter and moisture content investigated from tuber dormancy to dormancy break points in the two genotypes. Because Y-axis contains values for multiple parameters with different units, we did not attach unit to it.

Discussion:

Comment 8; The discussion is sometimes highly exaggerated in terms of putative regulation of sugars, trehalose-6-phosphate, SNRK1 activity and dormancy breaking (from L. 505 onwards). Without measuring the involved metabolites and gene expression the involved statements cannot be made. I suggest that the authors stick to the discussion of the results presented. In this regard it should be discussed, whether the observed increase of monosaccharides at dormancy breaking/bud emergence might be rather the sole consequence of re-mobilization of starch due to increased sink strength of the newly formed tuber buds.

Response; Nonreducing sugar which we measured comprises of trehalose-6-phosphate, sucrose, raffinose, verbascose and gentianose. We placed on emphasis on trehalose-6-phosphate and sucrose only during our discussion because information available in literature revealed that these two play significant roles in plant growth regulation. For SNRK1, literatures copiously reported that the transcript is a sugar signaling factor in plant, hence we speculated that it might be playing role as sugar status responsive signaling factor in yam tuber during dormancy-to-dormancy break period.

Comment 9; suggestion for extensive English language edition and later clarifications;

Dear Mr. Nwogha,

I hope you are doing well.

As we discussed yesterday, I am forwarding you the suggested corrections
from the reviewer regarding the English improvements.

Response to authors:

Dear authors: My suggestion to improve the language refers mostly to the
use of units and abbreviations. Please go through the entire manuscript
and check for the following issues:

- Add dashes or spaces between numbers and units for better readability
of the text. For example, “42DAPM” should be “42-DAPM”, “15days” should
be “15 days”, “50mg” should be “50 mg”, “5ml” should be “5 ml”. This
refers to all units in the manuscript. Exceptions are “s” (“seconds”), %
(percent) and M/N (Molar), which are shown without spaces behind values.

- Use the unit “ml” instead of “mL”

- Add spaces when mentioning Figures and subfigures. For example,
“Figure3a-f” should be “Figure 3a-f”. Unify Figure designations (Figure,
Fig, fig) throughout the manuscript.

- Unify designation of genotypes. For example, always use “Obiaoturugo”
instead of sometimes “TDrObiaoturugo” or “G2: Obiaoturugo”.

- Check the use of abbreviations. For example, you use the term
“appearance of shoot bud” three times fully written out and always place
the abbreviation (ASB) behind. In this case, the abbreviation can be
omitted then.

- Check whether “Trehalose”, “Trehalose-6P” or “tre6p” is correct.

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Good luck with the further revision. If you have any additional
questions, please don't hesitate to contact me.

Kind regards,

Response; the observations and suggestions made about units, figures, ASB and crosschecking of tre6p or trehalose-6-p correctness have all been taken and corrections done. However, we wish to appeal that the little differences observed in designation of Obiaoturugo which were corrected in the table and figures’ footnotes be permitted, because it came from the R scripts used for date analysis.

Once again, we appreciate the efforts editors and reviewers for painstakingly reading through the manuscript and making some valuable inputs which have extremely improved the quality of manuscript.

 

Yours sincerely

Jeremiah S. Nwogha

On behalf of the co-authors

Round 2

Reviewer 2 Report

The authors have sufficiently improved their manuscript. Congratulations!

However, I still feel that the integration of the SnRK and Trehalose-6-P signaling pathways into the discussion is too vague and in no way supported by the data. In my opionion there is no reason to integrate these issues into the discussion.