Testing the chilling‐ before drought‐tolerance hypothesis in Pooideae grasses

Abstract

With the rise of atmospheric CO 2 , current global average temperatures have increased by about 1°C compared to pre-industrial times (IPCC, 2021). As a result, we are experiencing increasingly severe drought and extreme weather events, the latter including unseasonal bouts of low and high temperatures that can adversely affect agricultural yield and lead to food insecurity (Cook et al., 2018;Craufurd

Drought tolerance as an evolutionary precursor to frost and winter tolerance in grasses

“…Strömberg 2011; Linder et al 2018). In light of this, the frost-first scenario for the BOP clade is surprising, but consistent with recent evidence from ecophysiological experiments and gene expression patterns in Pooideae (Das et al, 2023; Pal Stolsmo et al, 2024), and suggestions that Pooideae originated in emerging cool climate pockets present as early as the Late Cretaceous (Das et al, 2023; Hagen et al, 2019; Schubert et al, 2020). Therefore, it is likely that frost tolerance evolved before drought tolerance in the BOP clade.…”

“…Alternatively, high evolutionarily lability of drought tolerance (Table 2; Pal Stolsmo et al 2024) limits the accuracy with which we can reconstruct how cold and drought traits evolved relative to each other in this clade (Bromham, 2015). Thus, although it is likely that modern-day stress responses originated from shared ancient pathways (Das et al, 2023; Folk et al, 2020; Preston & Sandve, 2013), it is possible that the signature of those pathways is no longer be present in some clades.…”

“…There is strong ecological, genetic and physiological evidence that adaptations to low temperature and drought stress are not independent. On a cellular level, the dehydration caused by extracellular ice is virtually identical to dehydration stress caused by drought (Körner, 2016; Sakai & Larcher, 1987), and several genes involved in responses to cold and frost stress are also expressed during drought stress (Birkeland et al, 2021; Das et al, 2023; Schubert, Grønvold, et al, 2019; Zhong et al, 2018). Both periodic drought and winter present long periods without possibilities for photosynthesis, and plants need storage carbohydrates that can be hydrolysed to provide fuel to survive both of these conditions.…”

Evolution of frost and drought responses in cool season grasses (Pooideae): was drought tolerance a precursor to frost tolerance?

“…Even though the climate was generally warm, previous reconstructions suggest that Pooideae originated in the Palaeoarctic, in cool-climate pockets in the emerging Eurasian alpine orogeny. They were therefore possibly exposed to short-term cool conditions, but not prolonged winters (Das et al ., 2023; Gallaher et al ., 2022b; Schubert et al ., 2019b). However, there remains considerable uncertainty regarding the biogeographical origins and the level of cold exposure experienced by early Pooideae.…”