Significant advances have been made in the last years trying to identify regulatory pathways that control plant responses to boron (B) deficiency. Still, there is a lack of a deep understanding of how they act regulating growth and development under B limiting conditions. Here, we analyzed the impact of B deficit on cell division leading to root apical meristem (RAM) disorganization. Our results reveal that inhibition of cell proliferation under the regulatory control of cytokinins (CKs) is an early event contributing to root growth arrest under B deficiency. An early recovery of QC46:GUS expression after transferring B-deficient seedlings to control conditions revealed a role of B in the maintenance of QC identity whose loss under deficiency occurred at later stages of the stress. Additionally, the D-type cyclin CYCD3 overexpressor and triple mutant cycd3;1-3 were used to evaluate the effect on mitosis inhibition at the G1-S boundary. Overall, this study supports the hypothesis that meristem activity is inhibited by B deficiency at early stages of the stress as it does cell elongation. Likewise, distinct regulatory mechanisms seem to take place depending on the severity of the stress. The results presented here are key to better understand early signaling responses under B deficiency.

Flowering time is a relevant agronomic trait because is crucial for the optimal formation of seeds and fruits. The genetic pathways controlling this developmental phase transition have been studied extensively in Arabidopsis thaliana. These pathways converge in a small number of genes including FT, the so-called florigen, which integrates environmental cues like ambient temperature. Nevertheless, detailed and functional studies about flowering time in Brassica crops are scarce. Here we study the role of the FT Brassica rapa homologues and the effect of high ambient temperature on flowering time in this crop. Phenotypic characterization and gene-expression analyses suggest that BraA.FT.a (BraA02g016700.3C) is decisive for initiating floral transition; consequently, braA.ft.a loss-of-function and hypomorphic mutations result in late flowering phenotypes. We also show that high ambient temperature delays B. rapa floral transition by reducing BraA.FT.a expression. Strikingly, these expression changes are associated with increased histone H2A.Z levels and less accessible chromatin configuration of the BraA.FT.a locus at high ambient temperature. Interestingly, increased H2A.Z levels at high ambient temperature were also observed for other B. rapa temperature-responsive genes. Previous reports delimited that Arabidopsis flowers earlier at high ambient temperature due to reduced H2A.Z incorporation in the FT locus. Our data reveal a conserved chromatin-mediated mechanism in B. rapa and Arabidopsis in which the incorporation of H2A.Z at FT chromatin in response to warm ambient temperature results in different flowering time responses. This work will help to develop improved Brassica crop varieties with flowering time requirements to cope with global warming.