General discussion 6 221 A promising avenue for subsequent research involves extending the investigation to additional species. Firstly, expanding to the sister families of Solanaceae, and continuing outwards until the FR-responsive behaviour of the three TFs is lost. However, it would be very helpful to also establish the functionality of these three genes in shade avoidance, by for example making knockout lines and testing their FR-responsiveness. Alternatively, we could explore plants with different pith morphologies, or preferably a species lacking pith in its internodes. An example of different pith structure is the legume Vicia faba (Figure 6.1). This species exhibits a distinctive developmental pattern where pith development in different internodes progresses through different developmental stages, namely undergoing programmed cell death in the younger internodes. It would be also interesting to see if we can identify if FR-responsive pith elongation and internode elongation are uncoupled in any dicot species. Table 6.3 Summary of the evolutionary analysis of multiple species in SAS. Y means Yes, N means No, Up means upregulation. Species S. lycopersicum C. annuum S. melongena B. nigra A. thaliana P. sativum G. max Elongation in FR Y Y Y Y Y N (slow) Y Pith elongation Y Y Y Y N N Y TF expression in FR Up Up Up TF conservation (reference point) High High 6.4 CONCLUSION In summary, this thesis has delved into diverse facets of shade avoidance in non-model dicots. We covered the phenotypic changes including cellular morphology, tissuespecific transcriptome changes, hormonal regulation of internode elongation and SAURs in tomato. Then, we studied the conservation of FR-responsive behaviour of transcription factors and the pith elongation in dicots. Our examination highlighted unique growth patterns, underscoring the significance of such nuances in various plant species. It appears that tomato hormonal and TF regulatory networks in SAS have diverged from those of Arabidopsis. Looking forward, the pursuit of a deeper comprehension of transcriptional regulation, evolutionary conservation, and molecular mechanisms governing growth responses remain key foci in SAS research.
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