3.1 Plasticity of life history traits in response to elevated temperature and its correspondence with plasmotype diversity
We wished to examine the effects of plasmotype diversity on barley fitness including growth and productivity while growing under ambient vs. high temperatures and to examine the possible relationship between photosynthetic rhythm and growth plasticity. Previously, we described the generation and clock analysis of the ASHER doubled haploid population divided between carriers of the B1K-09-07 and B1K-50-04 plasmotypes. For the current study, we also developed a set of crosses between 11 wild barley accessions to achieve reciprocal hybrids lines (RHL) with few genotypes missing to achieve full half-diallel (see Methods).
In ASHER, under both HT and AT, carriers of the Hermon plasmotype flowered significantly earlier than the Ashkelon types. However, in both subpopulations, this manifested in the same thermal acceleration of flowering by more than two days (Figure 1a ; TableS2a ). The reproductive traits were higher under AT vs. HT conditions (avg spike dry weight (ASDW) =0.89 ±0.13 vs. 0.7 ±0.12 gr and Spikes dry weight (SpDW) =7.8 ±1.9 vs. 6.24 ±1.7 gr, respectively). Plant height (PH) at harvest was also higher under AT (124.9 ±8.5 cm) than under HT (108.1 ±7.8 cm), although vegetative dry weight (VDW) was lower under AT, i.e., 13.1 ±3.5 gr vs. 14.4 ±4.7 gr in HT (FigureS4a ). For SL, there was no significant difference between sub-populations (Figure 1b ). However, for the SLCV, Hermon plasmotype was linked to lower stability (Fridman 2015), i.e., higher CV under HT (14.45% under HT vs. 8.8% under AT) as compared to Ashkelon (12.33% under HT vs. 9.32% under AT) (Fig. 1c ). One interesting comparison is between the total vegetative and reproductive outputs. The carriers of the Ashkelon plasmotype are, on average, very plastic for the plant biomass and the derived total dry matter (Figure1d, e ). In contrast, the Hermon plasmotype carriers are relatively stable for the biomass yet respond significantly to the heat with significant reduction of the SpDW (Figure 1e, f ). This is in comparison to the relative stable SpDW of the Ashkelon types (Figure1f ).
Unlike in the ASHER’s case, in the RHL, DTF was almost identical between HT and AT (DTF=-109.9 ±5.6 and 111.73 ±4.97 days, respectively) (FigureS4b ). Similarly, unlike the significant effects of the thermal environment on the vegetative traits, the reproductive traits were less affected; ASDW is significantly yet mildly lower under AT (0.93 ±0.24 gr) than under HT (1.03 ±0.27 gr). For SpDW, there was not a significant difference between environments (7.13 ±2.2 and 7.35 ±3.16 gr, respectively). PH was also not significantly different between environments (104.06 ±10.17 cm in AT and 104.04 ±12.05 cm in HT), as compared to VDW and TDM that were significantly lower under AT (11.29 ±4 and 18.5 ±5.5 gr) than HT (16.38 ±6.8 and 24.13 ±9.08 gr). SL and SLCV are significantly lower under AT condition (Figure S4b ; TableS2b ). The reciprocal nature of the hybrids allowed us to group the F1 genotypes into different plasmotype subpopulations and different male parent subpopulations (representing the nucleotype). One-way ANOVA for each of these two divisions of the hybrids indicated a larger percentage variation explained (PVE) by the nucleotype (male donors) in comparison to differences between plasmotype (female donors) for a few traits (Table 1 ). For example, for the ASDW under HT the nucleotype factor explained 41% of trait variation (PVE=41%) vs. PVE=27% by the plasmotype. For most life history traits, however, we found higher variation explained by the plasmotype than by the nucleotype under both temperatures (AT and HT): for PH, PVE=39% vs. 30% and 33% vs. 21% under AT and HT, respectively. Higher variation explained by the plasmotype than nucleotype was true also for reproductive output, e.g., SpDW, which showed higher variance between plasmotypes under AT (PVE=35% vs. 21%) and to a lesser extent under HT (PVE=23% vs. 19% between plasmotype and nucleotype contributions).
To summarize, plants in both field experiments of the two populations accumulated more VDW on average at higher temperatures and showed lower stability between spikes, i.e., higher VDW and SLCV. The nature of the ASHER population allowed us to relate the positive correlation between increased biomass plasticity and stabilizing of the reproductive output with plasmotype diversity.