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).