General discussion 6 209 induced elongation. Then, finally in Chapter 5, we expanded our research from tomato to other dicots and explored the diversity of internode elongation in the shade avoidance response and the putative regulatory roles of specific GATA, TCP, and bZIP transcription factors identified in Chapter 3. The multi-species study unveiled diverse responsiveness to supplemental FR light across dicots, with quantifiable pith elongation observed in the species strongly responsive to the FR signal. The conservation of expression patterns of candidate TFs within Solanaceae suggests functional significance in this family. Distinct pith responses, indicated by cell-type-specific gene expression patterns of these TFs in some dicots (e.g. Solyc08g080150 homologs in Soybean, Figure 5.13), also indicate that pith responses are regulated differently to the rest of the internode, and that pith plays a specific role in SAS. Overall, this thesis offers novel insights into transcriptional regulation, evolutionary conservation, and molecular mechanisms shaping FR responses across dicots. Building on this, the thesis delves into the transcriptional regulation, evolutionary conservation, and molecular mechanisms governing FR responses across dicots. While the primary focus is on SAS in the physiological response of tomato crops, the evolutionary content enriches the scope of this study. In this general discussion chapter, I will bring together a number of topics that have emerged in the experimental chapters. Firstly, I will discuss the role of pith cells for stems, and what our findings in Chapters 2, 3 and 5 suggest as the relevance of pith in SAS. Then, I will discuss the role of different hormones in tomato SAS (Chapter 4), and how these might play integrate into the expression patterns of SMALL AUXIN UPREGULATED RNAs (SAUR)s we observed in Chapter 3. Finally, I will discuss TF evolution (Chapters 3 and 5) and conclude with general evolutionary hypothesis. 6.1 PITH IN SAS 6.1.1 What is pith? The pith is the central, often spongy, tissue found in the stems of vascular plants. It consists of large, loosely packed parenchyma cells, and its primary function is to store and transport nutrients throughout the plant. The pith is encircled by a ring of xylem, which is in turn encircled by a ring of cambium, and then a ring of phloem. In some plants, the pith may play a role in providing structural support to the stem (Venning, 1949; Esau, 1953; Hardwick and Elliott, 2016). The pith can vary in size, shape, and composition among different plant species, and often it faces programmed cell death, leaving a hollow internal cylinder. The pith’s cellular structure, specifically the arrangement and
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