Seasonal and microclimate-responsive expression of VRN-A1 and VRN-B1 in wheat under field conditions

The need of vernalisation, controlled by the gene VRN-1, impacts wheat adaptation and yield stability, yet field evidence on the plasticity of VRN-1 homoeologs expression is limited. We quantified VRN-1 homoeolog dynamics across two sites and two seasons in seven cultivars, by sampling their apex and leaf. VRN-A1 varied with genotype (P < 0.001***), tissue (apex > leaf; P < 0.001***), apex development (P < 0.001***), day length (P < 0.001***), and to a lesser extent, on short-term freezing exposure, quantified as a 5-day freezing-degree sum (FDS; P = 0.019*). Photoperiod class (Ppd-D1a vs Ppd-D1b) added an additional effect (P = 0.001***). VRN-B1 showed strong genotype effects (P < 0.001***), a modest effect of site on its expression (P = 0.025*), and pronounced associations with microclimate variables (day length, thermal sums, freezing exposure; all P < 0.001***). Directionally, Ppd-D1a backgrounds tended to advance the development while showing earlier apex VRN-A1 peaks. Overall, VRN-A1 expression mainly reflected developmental stage and seasonal forcing, whereas VRN-B1 might be more microclimate-responsive, indicating complementary roles for timing and stress-response plasticity. To isolate causal effects and to further explain these dynamics, targeted sequencing and tests in near-isogenic lines will be needed in future work.