111
S-transferase and cytochrome P450, which are not directly related to jasmonate
biosynthesis. The response to methyl jasmonate, mediated in G. imbricata by
enzymes, including 1-deoxy-d-xylulose 5-phosphate synthase, 1-deoxy-d-xylulose
5-phosphate-reductosisomerase, farnesyl diphosphate synthase and geranyl diphosphate synthase was also determined. The genes encoding these enzymes form part
of the mevalonate-phenylpropanoid- and tyrosine-derived pathways.
Unlike a genome comparison, the choice of a candidate gene to represent the
manifestation of a trait (i.e. cystocarp maturation, sporulation) could help to discern
the role of volatiles in reproduction. In particular the ornithine decarboxylase (ODC)
gene, which encodes the synthesis of the main protein (ODC, EC. 4.1.1.17), in
charge of polyamine biosynthesis has been a target gene for the study of reproduction in red seaweeds (Garcia-Jimenez and Robaina 2015).
When infertile G. imbricata thalli were treated with ethylene or methyl jasmonate
as elicitors of cystocarp development, different ODC expression patterns were
observed. Depending on the type of elicitors of cystocarp development, the ODC gene
expression was differentially correlated with the elicitation period or with the disclosure period (first visible developing cystocarps; Montero-Fernandez et al. 2016).
Moreover, transcription factor-related motifs and regulatory sequences related to
methyl jasmonate and ethylene have been identified in the 5′ upstream region of
ODC. Their functional involvement with this gene remains to be determined.
Obviously, the issue is still more complex owing to chemical diversity of volatile
compounds and to genes involved in biosynthesis and signalling pathways of different volatiles. Despite high-throughput data from seaweed which are enabling the
study of functional genomics with approaches about how gene regulation works, the
volatile receptors and signalling patterns of these volatile compounds in seaweed,
why some of the signalling patterns emerge instead of others and how we could
control them remain to be known.
We are aware that the understanding of genes represents the first step towards the
comprehension of seaweed system biology. However, this is not that easy. For
instance, seaweeds are subjected to extreme environmental conditions in which different gene pathways act, mainly some aiming to favour the release of spores in low
tide periods and others related to stress situations which are coincident with the
desiccation. In this sense to reach a complete awareness of system biology, an
exhaustive picture of gene network and interactions would be necessary.
We are far from this knowledge in seaweeds, but once the gene network is identified, the bridge between gene function and traits relevant to alga reproduction will
undoubtedly be of utmost interest to related events.
5.7 Conclusions
Overall, the information summarised here emphasises the myriad of volatiles emitted by seaweeds, which are classified according to their functional chemical groups.
Whereas a lot of basic information on the type of algal volatile emissions have
5 Volatiles in the Aquatic Marine Ecosystem: Ethylene and Related Plant Hormones…
S-transferase and cytochrome P450, which are not directly related to jasmonate
biosynthesis. The response to methyl jasmonate, mediated in G. imbricata by
enzymes, including 1-deoxy-d-xylulose 5-phosphate synthase, 1-deoxy-d-xylulose
5-phosphate-reductosisomerase, farnesyl diphosphate synthase and geranyl diphosphate synthase was also determined. The genes encoding these enzymes form part
of the mevalonate-phenylpropanoid- and tyrosine-derived pathways.
Unlike a genome comparison, the choice of a candidate gene to represent the
manifestation of a trait (i.e. cystocarp maturation, sporulation) could help to discern
the role of volatiles in reproduction. In particular the ornithine decarboxylase (ODC)
gene, which encodes the synthesis of the main protein (ODC, EC. 4.1.1.17), in
charge of polyamine biosynthesis has been a target gene for the study of reproduction in red seaweeds (Garcia-Jimenez and Robaina 2015).
When infertile G. imbricata thalli were treated with ethylene or methyl jasmonate
as elicitors of cystocarp development, different ODC expression patterns were
observed. Depending on the type of elicitors of cystocarp development, the ODC gene
expression was differentially correlated with the elicitation period or with the disclosure period (first visible developing cystocarps; Montero-Fernandez et al. 2016).
Moreover, transcription factor-related motifs and regulatory sequences related to
methyl jasmonate and ethylene have been identified in the 5′ upstream region of
ODC. Their functional involvement with this gene remains to be determined.
Obviously, the issue is still more complex owing to chemical diversity of volatile
compounds and to genes involved in biosynthesis and signalling pathways of different volatiles. Despite high-throughput data from seaweed which are enabling the
study of functional genomics with approaches about how gene regulation works, the
volatile receptors and signalling patterns of these volatile compounds in seaweed,
why some of the signalling patterns emerge instead of others and how we could
control them remain to be known.
We are aware that the understanding of genes represents the first step towards the
comprehension of seaweed system biology. However, this is not that easy. For
instance, seaweeds are subjected to extreme environmental conditions in which different gene pathways act, mainly some aiming to favour the release of spores in low
tide periods and others related to stress situations which are coincident with the
desiccation. In this sense to reach a complete awareness of system biology, an
exhaustive picture of gene network and interactions would be necessary.
We are far from this knowledge in seaweeds, but once the gene network is identified, the bridge between gene function and traits relevant to alga reproduction will
undoubtedly be of utmost interest to related events.
5.7 Conclusions
Overall, the information summarised here emphasises the myriad of volatiles emitted by seaweeds, which are classified according to their functional chemical groups.
Whereas a lot of basic information on the type of algal volatile emissions have
5 Volatiles in the Aquatic Marine Ecosystem: Ethylene and Related Plant Hormones…