## 1 Introduction  
With the rise in mean global temperatures, the earth's biosphere is warming up gradually. According to the statistics of the North American Space Agency's (NASA) earth observatory data, the average global temperature increased above 1 \({}^{\circ}\)C since the year 1880 [1]. In the next 100 years, the surface temperatures are expected to rise between 2 \({}^{\circ}\)C to 6 \({}^{\circ}\)C if greenhouse gas emissions continue. This is a serious threat for our future generations as it directly influences the habitable conditions--both flora and fauna. A rise in temperature induces heat stress and seriously affects plants, which play a key role in providing food, oxygen, and shelter to several species of fauna including humans. Moreover, its effects on the productivity of food crops will result in a food crisis for the growing population [2]. Recently, [PERSON] et al. (2017) [3] estimated that for every one-degree rise in global temperature, yields of food crops like wheat, rice, maize, and soybean will be reduced by 6%, 3.2%, 7.4%, and 3.1%, respectively [3]. Therefore, there is a grave need to understand the effects of increasing temperatures and the biological responses induced in food crops, to address challenges in developing next-generation crops [2; 3]. Heat stress damages both physiological and molecular level mechanisms in plants [4; 5; 6; 7]. Major damages include scorching and abscission of leaves, shoot and stems, fruit/seed damage, reduced photosynthesis, seed germination, increase in reactive oxygen species (ROS), and osmotic stress [5; 6; 8; 9; 10; 11]. Furthermore, the ROS accumulated during heat stress damages molecular components by inducing oxidative stress [12; 13]. For example, the formation of hydroxyl radicle could induce irreversible DNA single-strand breaks, peroxidation of lipids, protein proteolysis, and damage of photosynthesis system II [14; 15; 16]. In addition, hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) formed during heat stress could alter the balance between starch biosynthesis and degradation mechanisms by upregulation of starch degradation and downregulation of the biosynthesis genes. Additionally, plants also develop heat-tolerance by responding to heat stress by altering their gene expression and synthesizing specific heat shock proteins (HSPs), transporters, and enzymes. Rice (_Oryza sativa_), being one of the top three food crops produced and consumed by nearly 3.5 billion people around the world, has been well studied for its yield and quality with respect to changes in global temperatures. According to the Food and Agriculture Organization (FAO) of the United Nations, Asia is the largest producer of rice in the world (nearly 90%). The average rice production statistics between 1994-2018 show that China and India stand as the top two producers (193 and 140 million tons respectively), while Japan is ranked 10 th (11 million tons) in the world. Japan is also the 13 th largest consumer of rice in the world as of 2018. In Japan, as rice is a primary staple food crop with high socio-economic importance, any reduction in yield and damage to the quality of the grain is a serious issue. The decrease in rice productivity is generally due to reduced pollen germination and in turn, affects the spikelet fertility and yield [17; 18; 19; 20; 21]. Moreover, spikelet sterility occurs when air temperature reaches a threshold limit of 35 \({}^{\circ}\)C during flowering time [22]. For example, in 2007, the Kanto and Tokaido regions of Japan faced a marked rise in temperatures to 40 \({}^{\circ}\)C during the summer months. The samples collected in this region showed high rates of spikelet fertility damages [19]. In addition to high-temperature injury in grain productivity, it also affects the quality of rice. For example, if rice crops are exposed to high temperatures during the first two weeks after an early emergence, the rice grain turns into immature kernels with white portions [23; 24; 25; 26].