Fig. 6: Restraining seed growth affects endosperm nuclei number.

a Perimeter of ant-T^−/−, klu-4^−/− and xxt1^−/− xxt2^−/− seeds comparatively to the respective WT at 2 days after pollination (DAP). Significance of difference was determined by one-way ANOVA. b Endosperm nuclei number of ant-T^−/−, klu-4^−/− and xxt1^−/− xxt2^−/− seeds comparatively to the respective WT at 2 DAP. Significance of difference was determined by one-way ANOVA. ***p < 0.0001, ***p < 0.001, **p < 0.01 and *p < 0.05. Error bars indicate standard deviation. The number below each sample indicate number of seeds analyzed. c Correlation between the number of endosperm nuclei and seed size at 2 DAP in different genotypes analyzed in this study. d Effect of a 24 h compression of the fruit with a microvice on seed size, endosperm size and number of endosperm nuclei in WT seeds at 2 days after pollination (DAP). Significance of difference was determined using one-way Wilcoxon tests. ****p < 0.0001, ***p < 0.001, **p < 0.01 and *p < 0.05. Error bars indicate standard deviation. For the control condition, 177 seeds were analyzed, and for the compressed condition, 130 seeds (two independent experiments). e Correlation between the number of endosperm nuclei and seed size, between the number of endosperm nuclei and endosperm size, and between endosperm size and seed size, in WT seeds at 2 DAP whose fruits were compressed for 24 h, as seen in (d). Smoothing of the data (colored lines) was done using a linear model. f Proposed model. Left, BRs create a permissive environment for seed coat expansion, which impacts endosperm proliferation. The mechanism by which this environment impacts auxin activity remains undiscovered (question mark). Right, loss of BR leads to a stiffening of the seed coat cell walls, which indirectly affects auxin activity in the endosperm, reducing its proliferation rate.