4.1 Whole plant and circadian clock responses to high temperatures and their interrelationship vs pleiotropy
In this study, we found significant responses of plant growth and clock rhythmicity under elevated temperature. Comparison between early and late growth phenotypes showed that plants growing in high temperatures initially gain some growth advantage, as reflected by the higher tiller heights measured at about one month after transplanting. However, at the final time of harvest the heat correlated significantly with reduced height, biomass and reproductive output (Figure S4 ). In addition, we found that heat is related with loss of robustness of the growth as could be viewed in the significant elevated CV of the spikes. Interestingly, the population of inbreds (ASHER DH) seemed to be more affected than the RHL, with the latter maintaining, for example, a similar mean for PH and SL values. These differences in the stability of hybrids was reported in many plant species and might be related with higher allelic heterogeneity across the genome (Fridman 2015), which to some extent may allow the plant to show a wider reaction norm as suggested in biochemical models of heterosis (Goff, 2011).
The experiments we describe in this study were all making use of wild barley plants and their derivatives. Although wild and cultivated barley belong to the same primary gene pool and easily crossed to obtain fertile interspecific populations (Wendler, 2018), the comparison between the results of current study to the one conducted with interspecifc HEB population raise at least one interesting difference in the adaptive behavior of the plants. In the previous study (Prustyet al., 2021), we identified a significant pleiotropy of theDOC3.2 , a locus that affected thermal plasticity of the vegetative growth and the clock amplitude. Carriers of the wild alleles showed increasing amplitude under higher temperature, and at the same time increased biomass but with lesser grain yield. Here, while analyzing the relationship between plasmotype diversity to clock and fitness traits plasticity we identified a different trend. There was an opposite relationship between plasticity of growth and reproductive output; under higher temperature increased biomass (and more pronounced plasticity of the clock) was correlated with stability of the reproductive output (Figure 1 ). The carrier of the B1K-50-04 plasmotype that kept stable growth under higher-temperature had a significant loss of average spike weight. These differences indicate that while wild alleles have the potential to benefit crop plants as often proposed (Dakhiya & Green, 2023), the interactions of the nuclear and plasmotype diversity should be tested in the relevant genetic and management “environments”. This approach is now followed in a new interspecific cytonuclear multi-parent population (CMPP) that we are currently testing for clock and for agricultural performance (manuscript in preparation).