Chapter 5 162 ABSTRACT This chapter explores the diversity of internode elongation responses to supplemental far-red light, delving into pith cell elongation, and the regulatory roles of specific GATA, TCP, and bZIP transcription factors (TFs). First, we extended our phenotypic investigation from tomato to eight dicots and found that they are diverse in responsiveness to treatment with supplemental far-red (FR) light. We also revealed quantifiable pith elongation happening in species with strong response to the FR signal. We followed up with the expression of three candidate transcription factor genes that had FR-responsive pattern in pith and/or internode in tomato. We identified the homologs for the genes encoding these transcription factors from each of the species, quantified their FR-responsive expression in internodes and piths, and found that the expression patterns were conserved within Solanaceae. In our study into pith in shade avoidance in these species, we saw the gene expression patterns that differed from the whole internode, indicating that the pith responses are distinct, likely cell-type-specific. Looking ahead, the pursuit of insights into transcriptional regulation, evolutionary conservation, and molecular mechanisms governing FR responses across dicots remains an interesting line to follow. Our work has started to shed light on the functional divergence and conservation of the factors that respond during shade avoidance.
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