## 2 Results and Discussion
### High Temperature-Triggered Regulatory Events in Koshiiukari Rice Seeds of Grades 2 and 3
#### 2.4.3 Transcription Factor Activation  
Besides differential expression of major genes involved in the metabolic process, several changes in the TF genes related to abiotic-stress responses were also observed. Specifically, in both Y2 and Y3 the MYB and bZIP TF's were downregulated while upregulation of AP2/ERF and OsWRKY was observed only in Y3 (Supplementary Table S4, Aiotic-Biotic stress; Figure 6). MYB4 TF-related gene (Os09g36730.1) was downregulated in both Y2 and Y3. Recent studies in _Arabidopsis_ have indicated that upregulation of MYB4 TFs induce the biosynthesis of secondary metabolites (hydroxycinnamate esters) that in turn increase UV-B hypersensitivity in plants [57; 58]. Downregulation of these MYB4 TFs in Y2 and Y3 indicate increased tolerance to UV-B radiation. AP2/ERF TFs were upregulated in Y3 alone. The AP2/ERF (APETALA2/ethylene response factor) TF's are one of the most important groups in plants that help in the stress defense mechanism [59]. These TF's induce a set of abiotic stress-related genes. In this study, AP2/ERF family proteins like dehydration-responsive element-binding protein (DREB1/CBF) (Os09g35020.1 and Os09g35010.1) and ethylene-responsive element-binding factor (ERF) (Os04g46220) were upregulated in Y3. These genes were known to play a key role in ABA independent stress tolerance, especially related to osmotic stress [60; 61]. The other major class of TFs identified in this study is the OsWRKY TFs. The WRKY TF's are well known for their roles in the regulation of plant growth, development and apoptosis, and responses to biotic and abiotic stresses [62]. There are 74 and 109 WRKY members in each of _Arabidopsis_ and rice genome, respectively [63; 64]. In the current analysis, especially in Y3, an upregulation of OsWRKY genes 24, 28, 45, and 49 (Os01g61080.1, Os06g44010.1, Os05g25770.1, Os05g49100.1), and downregulation of OsWRKY24 (Os07g02060.1) was observed. However, no such specific responses were observed in Y2. Among these, the OsWRKY28 and OsWRKY45 were well studied. OsWRKY28 known to be highly responsive to As(V) and regulation of As(V)/Pi uptake or tolerance in rice [65]. In addition, [PERSON] et al. (2014) showed that OsWRKY28 rice mutants resulted in various disorders like downregulation of JA biosynthesis genes in the shoots, irregular spikelet development, altered flower closing, and another dehiscence and eventually resulting in lower fertility [66]. In the current study, JA gene expression was observed to decrease in Y2 while OsWRKY28 is not differentially regulated. On the other hand, in Y3, upregulation of OsWRKY28 along with JA biosynthesis genes is seen. In addition, JA is also known to regulate OsWRKY45 gene expression [67]. The OsWRKY45 family is also known to participate in ABA and salt stress signaling [68]. Therefore, it is obvious from our study that the expression of OsWRKY28, JA, and OsWRKY45 are linked to each other. This clearly indicates that Y3 might be moving towards heat stress damage recovery by overexpressing these TFs and in turn producing stress-responsive hormones.