Apocarotenoids as Stress Signaling Molecules in Plants

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

The text brings very relevant information on aspects of the physiology of signaling in plants. It is clearly written and easy to understand. I just have few points to highlight, as the inclusion of an ‘Introduction’ and suggestion on improvements of Figure´s titles:

1. I recommend including an introduction before the item “1. Carotenoids” providing and overall view of the items treated in the manuscript. It could be an expansion of the current abstract.
2. In the title of Figure 1, please include also the list of main carotenoids present in the cyanobacteria-like organisms.
3. In Figure 2, the title could be improved by changing “Apocarotenoids with enzymatic biosynthesis and with an already identified receptor” by “Pathways of enzymatic biosynthesis of apocarotenoids with an already identified receptor”.
4. In Figure 3, the title “Oxidative origin of Apocarotenoids. A new hypothesis suggests that apocarotenoids may originate also independently of singlet oxygen, by direct energy transfer from triplet chlorophyll to triplet β-carotene in the extended PSII” could be replaced by “Hypothetical pathways of the oxidative origin of Apocarotenoids by direct energy transfer from triplet chlorophyll to triplet β-carotene in the extended PSII, independently of singlet oxygen”.
5. In Figure 4, the title “β-carotene apocarotenoids with mainly oxidative biosynthesis and without an identified receptor” could be replaced by “Biosynthesis pathways of β-carotene apocarotenoids via a mainly oxidative process that do not have an identified receptor”.

Author Response

We greatly appreciated the comments and suggestions of Reviewer 1 and we thank them for their help in improving the manuscript.

• [I recommend including an introduction before the item “1. Carotenoids” providing and overall view of the items treated in the manuscript. It could be an expansion of the current abstract.]

We added a brief introduction section in the beginning to provide a view of the subjects treated in the review. Lines 25-32

• [In the title of Figure 1, please include also the list of main carotenoids present in the cyanobacteria-like organisms.]

We added a sentence on characteristic cyanobacteria carotenoids (lines 50-53) and modified the title of Figure 1 as suggested

• [In Figure 2, the title could be improved by changing “Apocarotenoids with enzymatic biosynthesis and with an already identified receptor” by “Pathways of enzymatic biosynthesis of apocarotenoids with an already identified receptor”.]

We modified the tile of Figure 2 as suggested

• [In Figure 3, the title “Oxidative origin of Apocarotenoids. A new hypothesis suggests that apocarotenoids may originate also independently of singlet oxygen, by direct energy transfer from triplet chlorophyll to triplet β-carotene in the extended PSII” could be replaced by “Hypothetical pathways of the oxidative origin of Apocarotenoids by direct energy transfer from triplet chlorophyll to triplet β-carotene in the extended PSII, independently of singlet oxygen”.]

We modified the tile of Figure 3 as suggested

• [In Figure 4, the title “β-carotene apocarotenoids with mainly oxidative biosynthesis and without an identified receptor” could be replaced by “Biosynthesis pathways of β-carotene apocarotenoids via a mainly oxidative process that do not have an identified receptor”.]

We modified the tile of Figure 4 as suggested

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript provides a comprehensive review of apocarotenoids with focusing on their roles as signaling molecules in plants. The authors synthesize current knowledge, highlight gaps in understanding, and propose future research directions. The manuscript is ambitious in scope, detail in content, and rich in citations. The discussion on how apocarotenoids could enhance crop resilience is compelling and relevant to current agricultural and climate challenges.

Figures need more detailed and self-contained legends. In addition, the manuscript uses many abbreviations (e.g., APO(-)7, APO9, dhA) without always defining them upon first use. Inconsistent abbreviations: e.g., “β-cc,” “β-cyclocitral,” and “Bcc” are used interchangeably. A glossary or table of abbreviations would be helpful. Pease also add a figure summarizing the signaling interactions between apocarotenoids and key phytohormones.

Author Response

We greatly appreciated the suggestions of Reviewer 2 and we thank them for their help in improving the manuscript.

• [Figures need more detailed and self-contained legends].

We expanded the description of all figures and changed the titles accordingly to Reviewer 1 and 2 suggestions.

• [In addition, the manuscript uses many abbreviations (e.g., APO(-)7, APO9, dhA) without always defining them upon first use. Inconsistent abbreviations: e.g., “β-cc,” “β-cyclocitral,” and “Bcc” are used interchangeably. A glossary or table of abbreviations would be helpful.].

We carefully reviewed the manuscript and ensured that all abbreviations are expanded upon their first use. While we did not include a comprehensive glossary for the various abbreviations commonly used in the literature to refer to apocarotenoids, we have associated each abbreviation with the full name of the corresponding molecule in the title of each subchapter in Section 6.

• [Please also add a figure summarizing the signaling interactions between apocarotenoids and key phytohormones.]

We have added a figure (Figure 5) summarizing the roles of apocarotenoids in stress responses and revised the manuscript title to better reflect our focus on stress signaling rather than developmental processes.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript entitled 'Apocarotenoids as signal molecules in plants' is nicely written by the authors, but they primarily focused on the biosynthesis of apocarotenoids in plants. I would suggest improving the manuscript in the following points:

1. The role/functional importance in pathways like photosynthesis, biotic and abiotic stress tolerance, etc. must be added.
2.  The figures are also designed for their oxidation/catalytic origin, but their roleplay in different signalling pathways must be addressed.
3. If authors can arrange some information in table format.
4. In some statements, references are missing. Kindly add these.
5. Some typo errors must be corrected as noted in the attached file

Comments for author File: Comments.pdf

Author Response

We thank Reviewer 3 for its suggestions and careful reading of the manuscript.

• [The manuscript entitled 'Apocarotenoids as signal molecules in plants' is nicely written by the authors, but they primarily focused on the biosynthesis of apocarotenoids in plants.].

We appreciate Reviewer 3’s observation. The manuscript is indeed structured to distinguish between the biosynthesis of apocarotenoids (Chapters 3, 4, and 5) and their signaling roles (Chapter 6). We placed particular emphasis on the biosynthetic pathways, as there is a significant distinction between apocarotenoids formed enzymatically and those generated through direct oxidation by reactive oxygen species (ROS). Moreover, our focus was specifically on apocarotenoids derived from β-carotene that lack a currently identified receptor, and their potential involvement in plant stress responses.

• [I would suggest improving the manuscript in the following points: The role/functional importance in pathways like photosynthesis, biotic and abiotic stress tolerance, etc. must be added.]

We clarified the signaling properties and the functions of beta/carotene derived apocarotenoids in chapter 6.

• [The figures are also designed for their oxidation/catalytic origin, but their roleplay in different signalling pathways must be addressed.]

We agree with Reviewer 3 that the manuscript was imbalanced toward the biosynthesis of apocarotenoid. Therefore, we added a figure summarizing apocarotenoid functions.

• [If authors can arrange some information in table format.].

We added a table to summarize cyclic apocarotenoids deriving from beta carotene and zeaxanthin (table 1)

• [In some statements, references are missing. Kindly add these.]

We added the references where suggested.

• [Some typo errors must be corrected as noted in the attached file].

We followed the suggestion by Reviewer 3 and corrected the following:

Line 78-80 The sentence has been rewritten as suggested.

Line 99-100 “chemical origin” has been changed with “without an identified receptor”

Line 249 We revised the text to clarify that we are referring to the protein, not the gene.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have incorporated all the modifications asked for improvement; thus can be accepted