9. BIOengineering CROPS FOR HIGH TEMPERATURE TOLERANCE
Several crop bioengineering approaches have been used in recent years to improve high temperature tolerance. For example, generating a nuclear origin supplementation pathway of the D1 protein (one of the core proteins involved in PSII repair system) to enhance rice photosynthesis by maintaining the capability of PSII repairment under heat stress (Chen et al., 2020). Additionally, thermostability of Rca is considered as a promising way to improve photosynthesis and thermotolerance for crops exposed to warmer temperature or heat stress (Scafaro et al., 2019). For example, introduction of Rca from maize into rice slightly improves the thermotolerance with respect to photosynthesis (Yamori et al., 2012), but the underlying reasons are not clear. For the rate of regeneration of the CO2 acceptor - RuBP, overexpressing a rice sedoheptulose-1,7-bisphophate (SBPase) in rice (Feng et al., 2007) or a bifunctional cyanobacterial fructose-1,6-bisphosphatase (FBP)/SBP in soybean under elevated temperature significantly increases carbon assimilation (Kohler et al., 2017). Additionally, C2 or C4 plants suffer less net carbon loss from photorespiration due to the carbon concentrating mechanisms (Bellasio & Farquhar, 2019; Keerberg, Parnik, Ivanova, Bassuner, & Bauwe, 2014; Kennedy & Laetsch, 1974; Khoshravesh et al., 2016). It is, therefore, likely that engineering C2 or C4 photosynthesis into C3 crops could have a large impact on crop production at high temperature (Bellasio & Farquhar, 2019; Lundgren, 2020).
Since daily temperature generally peaks at noon, which overlaps with the flowering time in some crops, one of the countermeasures is an effective heat escape mechanism (Jagadish, 2020). Therefore, naturally or genetically introducing flowering traits towards cooler times of day can potentially minimize heat stress damage on reproductive organs. Some dryland crops are able to optimize their anthesis during morning or cooler evening periods under heat stress (Aiqing et al., 2018; Bheemanahalli et al., 2019). In contrast, most rice varieties need the genetic introduction of early morning flowering trait to shift their flower opening time (Bheemanahalli et al., 2017; Jagadish, 2020).
Finally, high-temperature plant resistance to fugal disease, caused by stripe rust (Puccinia striiformis f. sp. Tritici,Pst ) has been successfully used to develop durable resistant wheat cultivars (Tao et al., 2020; Uauy et al., 2005; Wang, H. Shang, et al., 2019; Wang et al., 2017; J. Wang et al., 2017; J. Wang et al., 2019; Zhou et al., 2014).