Exploring conservation of cellular-level traits in shade avoidance syndrome among species 5 167 conservation of FR-responsiveness, we used an interspecies analysis with the homologs of three FR-responsive TFs we discovered in tomato in Chapter 3. First, Solyc01g090760 encodes a GATA TF, belonging to the zinc finger DNA binding protein family. A GATA homolog in humans is vital for development and cell differentiation (Gao et al., 2015; Lu et al., 2021; Hou et al., 2022). Second, Solyc08g080150, or SlTCP20, encoding for a TCP transcription factor, exhibits diverse functions in leaf development, flower symmetry regulation, shoot branching, and senescence (Cubas et al., 1999; Parapunova et al., 2014). Third, Solyc07g053450, encodes a bZIP transcription factor which plays a pivotal role in various biological processes, particularly abiotic stress responses (Liu et al., 2023a). We carried out an homology analysis and qPCR analysis to see if the FRinduced expression in internodes was conserved. The investigation strived to illuminate the connection between TFs, SAS, and the development of essential plant structures, providing insights into how various plant species acclimate and thrive in response to shifting light condition. 5.2 RESULTS 5.2.1 Arabidopsis inflorescence stem elongates in response to lower R:FR ratio in long day conditions Arabidopsis thaliana accession Col-0 is widely used to study petiole elongation and leaf hyponasty in SAS (Kohnen et al., 2016b; Müller-Moulé et al., 2016; Michaud et al., 2017; Pantazopoulou et al., 2017). However, there is limited information on the elongation of inflorescence stem, that undergoes major secondary growth, in response to environmental cues such as FR enrichment. We wanted to test if the tomato stem FR responses were conserved in Arabidopsis and if we could use the wide Arabidopsis genetic resources for dissecting our tomato radial growth and pith findings. In tomato supplemental FR treatment, a long day condition of 16 hours of daylight and 8 hours of darkness with 200 PAR is typically used. In Arabidopsis experiments in our group, a lower light level ranging from 120 PAR to 150 PAR before flowering is used, and plants are usually subjected to short day conditions. Therefore, we needed to test if specific conditions, if any, were suitable for inducing stem elongation FR-response in Arabidopsis. We conducted a FR treatment with bolted inflorescence stems measuring 0.5-1.5 cm. We first tested the effect of day length: long day (LD, 16h light, 8h dark) or short day (SD, 8h light, 16h dark). We started with R:FR (“WL+FR”) of 0.2 in SD with 150 PAR, same R:FR ratio as we tested tomato. Inflorescence stem elongation response was
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