## 2 Results and Discussion
### High Temperature-Triggered Regulatory Events in Koshiiukari Rice Seeds of Grades 2 and 3
#### 2.4.2 Lipid Remodelling  
The lipid signaling is another key process involved in abiotic stress responses by the plants. In Y2, there is no more than one gene related to lipid mechanism which was identified as the HRDEgene. This gene (Os08g04800.1) codes for a TAG lipase protein and is related to lipid degradation. TAG lipase was found to be strongly downregulated (-1.63). TAG lipases de-esterify fatty acids from TAG (accumulated in lipid bodies) or plastglobular lipids and are generally accumulated during seed germination [45]. TAG lipases are observed to be accumulated under heat stress in _Arabidopsis_[45; 46]; however, the current data shows the opposite result. It is to be noted that rice and _Arabidopsis_ are different, and therefore, the same gene could have unique functions in different plants and tissues. On the other hand, in Y3 there were no genes related to TAG lipases identified as HRDEs. However, the same gene was found in Y3 with very minimal (three times less than Y2) downregulation (not HRDE). This indicated that in this case, strong downregulation of TAG lipases could be common in Koshihikari as this is a DEG analysis in comparison to Y1 also. So, the result in Y3 indicates that Y3 might have started the accumulation of this gene under heat stress.  
Furthermore, the genes related to diacyl-glycerol kinases (DGK), phospholipid synthesis, sphingolipid transferases, and fatty acid omega 6 desaturases were strongly upregulated in Y3 (supplementary Table S3, Metabolism overview; and Figure 5). In general, DGKs are involved in phosphatidic acid (PA) synthesis as well as sphingo-lipid synthesis. The PA produced by the mediation of DGKs has a positive regulatory impact on sphingo-lipid kinases and a negative effect on abscisic acid synthesis pathways [47]. PA is also involved in the growth and development of plant root hair and also functions as membrane-localized signal to recruit specific proteins and change their activity [48; 49; 50]. Therefore, by upregulation of this DGK specific gene (Os04g54200.1), Y3 is preparing for abiotic stress due to increased temperatures.  
The fatty acid desaturases, on the other hand, are involved in maintaining membrane fluidity and are usually upregulated under low-temperature stress. However, studies also identified that high temperatures also enhance desaturases involved in the eukaryotic pathway [51]. In the current work upregulation of omega-6-desturases (Os07g23410.2, Os07g23430.1, Os02g48560.5) FAD2 and FAD3 related genes was observed. This clearly indicates a remodeling of fatty acids in endoplasmic reticulum [52]. In addition, the FAD2 gene was also found to be downregulated. This could be possibly due to a stop in the FA 18:1 synthesis from plastids [53; 54].  
Sphingo-lipids, on the other hand, also play an essential role in preventing plants from heat stress. Therefore, the data were screened for any changes in Sphingo-lipid genes and resulted in the identification of an upregulated of serine palmitoyl transferase 2 (SPT2) (Os01g70370.1) in Y3. This enzyme is involved in de novo synthesis of sphiganine and di-hydro shpinganine to form sphingo-lipids and ceramides. The ceramides further induce at least one heat shock protein-like \(\alpha\beta\)-crystallin upon heat stress [55]. In accordance with this, an upregulation of \"\(\alpha\)-crystallin-Hsps IbpA,\" a small Hsp (sHsp) related gene (Os02g48140.1) was also observed (Supplementary Table S4, Aiotic-Biotic stress; Figure 6). The SPT2 enzyme is known to play a key role in the male gametophyte development in _Arabidopsis_[56]. Upregulation of SPT2 might be a heat shock recovery mechanism in order to prevent gametophyte damage.