Abstract
The phytohormone auxin plays a critical role in plant development, including embryogenesis, organogenesis, tropism, apical dominance and in cell growth, division, and expansion. In these processes, the concentration gradient of auxin, which is established by polar auxin transport mediated by PIN-FORMED (PIN) proteins and several ATP-binding cassette/multi-drug resistance/P-glycoprotein (ABCB/MDR/PGP) transporters, is a crucial signal. Here, we characterized the function of ABCB19 in the control of Arabidopsis organ boundary development. We identified a new abcb19 allele, abcb19-5, which showed stem-cauline leaf and stem-pedicel fusion defects. By virtue of the DII-VENUS marker, the auxin level was found to be increased at the organ boundary region in the inflorescence apex. The expression of CUP-SHAPED COTYLEDON2 (CUC2) was decreased, while no obvious change in the expression of CUC3 was observed, in abcb19. In addition, the fusion defects were greatly enhanced in cuc3 abcb19-5, which was reminiscent of cuc2 cuc3. We also found that some other organ boundary genes, such as LOF1/2 were down-regulated in abcb19. Together, these results reveal a new aspect of auxin transporter ABCB19 function, which is largely dependent on the positive regulation of organ boundary genes CUC2 and LOFs at the postembryonic organ boundary.
Highlights
Throughout the lifespan of most higher plants, new organs are initiated continuously from pluripotent cells in the shoot apical meristem
These results reveal a new aspect of auxin transporter ABCB19 function, which is largely dependent on the positive regulation of organ boundary genes CUP-SHAPED COTYLEDON2 (CUC2) and LOFs at the postembryonic organ boundary
Organ fusion defects occurred at both stem-cauline leaf junctions (Figure 1F and G) and stem-pedicel junctions (Figure 1H and I)
Summary
Throughout the lifespan of most higher plants, new organs are initiated continuously from pluripotent cells in the shoot apical meristem This essential process is associated with the establishment of boundaries separating the newly formed organs from adjacent tissues [1]. The unique shape of these cells is attributed to elongation along the organ boundary, contraction along the axis perpendicular to the boundary, and cell division leading to a new cell wall parallel to the boundary [2,3,4] These boundaries emerge at the early stage of primordia initiation, and their positions are determined by signals from the central region of the meristem [1,2,5]. The boundaries act as a barrier to separate and maintain different cell types [1], and, when localized at the base of leaves, they have the potential to produce axillary meristems, which contribute greatly to the overall architecture of plants [6]
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