Chapter 3 84 elongation(Ma and Li, 2019; Stortenbeker and Bemer, 2019) Additionally, SAUR genes can be regulated by various factors, including auxin and other environmental cues, and their overexpression has been shown to induce growth, indicating their significant role in plant development. Furthermore, SAUR proteins are involved in the induction of growth via cell elongation, and their activity is not limited to the juvenile stage but extends to various tissues, indicating their widespread function in plant growth and development (Stortenbeker and Bemer, 2019). Therefore, SAUR proteins act as effectors of hormonal and environmental signals in plant growth, with their main function being the induction of cell elongation by repressing PP2C.D activity and promoting cell expansion (Ma and Li, 2019; Stortenbeker and Bemer, 2019). Furthermore, SAUR gene expression is subject to regulation by various factors in different species. Studies in tomato, cotton, poplar, citrus, watermelon, maize, and Arabidopsis have unveiled specific expression patterns for different SAUR genes throughout plant development. Additionally, the expression of distinct sets of SAUR genes can be either positively or negatively regulated by multiple hormones, including auxin, cytokinin, gibberellic acid (GA), brassinosteroids, ethylene, ABA, and JA, as well as by varying light conditions, temperature, and stress factors in different plant species. In general, SAUR genes tend to be upregulated in response to growth-inducing factors like auxin and downregulated under stress conditions or in response to growth-inhibiting hormones such as ABA and JA. This dynamic regulation likely represents a plant’s adaptive strategy to balance growth and defense mechanisms (Knauss et al., 2003; Franklin et al., 2011; Walcher and Nemhauser, 2012; Qiu et al., 2013; Stamm et al., 2013; Luo et al., 2018). Notably, the responsiveness of SAUR genes to environmental and hormonal cues primarily occurs in the tissues where they are already expressed, emphasizing their tissue-specific expression patterns (Hagen and Guilfoyle, 2002; Markakis et al., 2013; Ren and Gray, 2015; van Mourik et al., 2017). Overall, the upregulation of SAURs in response to shade conditions is believed to be an important component of SAS by promoting cell elongation, allowing plants to modulate their growth and development in response to changing light conditions. 3.3.2 Much of the variance of expression data is due to diurnal rhythm FR effect on elongation of tomato first internode was seen at two days (Figure 3.1), considerably slower than the FR effect on elongation of petiole of Arabidopsis (Walter et al., 2007; Ciolfi et al., 2013; Morón-García et al., 2022). Therefore, based on our data
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