Skip to main content
. 2021 Nov 30;12(12):1936. doi: 10.3390/genes12121936

Figure 2.

Figure 2

Overview of the role of basal ABA in stomata development, cuticle and suberin deposition, and xylem differentiation. Genetic analysis of ABA synthesis and signalling demonstrates a role for basal ABA in stomatal development, protoxylem differentiation, and deposition of cuticle and suberin. (a) ABA biosynthetic and signalling mutants show increased stomatal index or density, while ABA catabolism mutant display decreased stomatal index or density, indicating a negative role for ABA in stomatal development. (b) ABA promotes protoxylem differentiation through upregulation of miR165/166 in the endodermis, which downregulates HD-ZIP III in the stele. Xylem differentiation is disrupted in ABA biosynthesis and signaling mutants, which develop discontinuous metaxylem strands. (c) ABA promotes cutin deposition, by indirectly regulating wax and cutin-related genes. In Arabidopsis and tomato ABA biosynthetic mutants, hydrophobic cutin and wax layers are reduced. In Arabidopsis, ABA signaling mutants display increased cuticle permeability. (d) ABA positively regulates suberin deposition. ABA biosynthetic and signaling mutants show decreased suberin accumulation. ABA regulates several MYB TFs, which in turn promote suberin or cuticle deposition. Other hormones also regulate these processes: ABA regulates suberin accumulation antagonistically to ethylene, while acting in parallel with auxin in xylem differentiation. ABA related mutants are shown in green for Arabidopsis and in magenta for tomato; ethylene and auxin mutants are shown in lilac/purple. Panels (a) and (c) abbreviations: MMC, meristemoid mother cell; GC, guard cell; UE, upper epidermis; PM, palisade mesophyll; SM, spongy mesophyll; LE, lower epidermis. Panels (b) and (d) abbreviations and legend: epidermis (Ep), light green; cortex (Co), light pink; endodermis (En), light orange; suberin lamellae (Sl), orange; Casparian strip (Cs), red; pericycle (Pe), light blue; procambium (Pr), grey; phloem (Ph), white; protoxylem (Px), purple; metaxylem (Mx), light purple/lilac. Figure created with BioRender (https://biorender.com/, accessed on 27 November 2021).