Abscisic acid, abiotic stress, and their interaction

The plant hormone abscisic acid (ABA) plays a pivotal role in regulating seed development, dormancy, stomatal closure, and stress tolerance (Fig. A). ABA also affects heterophylly, different types of leaf in a plant, in the lily (a geophytic plant) through differential expression of 9-cis-epoxycarotenoid dioxygenase 3 (NCED3), a key gene in ABA biosynthesis. Moreover, antagonism between ABA vs. ethylene and ABA vs. GA affects seed germination, seedling growth, and leaf development. These hormones may control the hormonal biosynthesis, catabolism, or signaling of each other to enhance their antagonism.

For study of abiotic stress, ten salt hypersensitive (sahy) mutants (Fig. B) were isolated by screening T-DNA tagged seeds on high salt-containing media. Of which, both sahy1 and sahy9 revealed strong salt oversensitivity and plant growth defect, including small plant size, short root, and pointed leaves. These two proteins are mainly localized to the nucleolus and have roles in ribosomal biogenesis/assembly, which might change ribosome composition and cause differential or preferential translation. They showed auxin-mediated developmental defects in leaf vascular pattern, arrangement of palisade mesophyll cells, and auxin transport and response. In addition, they also affected salt sensitivity at least through ABA-dependent, ABA-independent, and salt-responsive gene expression.

To further dissect the components involved in ABA signal pathway and crosstalk with stress signal pathways, we have isolated several aba2 suppressor (abs) mutants (Fig. C) based on their response to high glucose and salt sensitivity. These abs mutants with ABA deficiency showed different soil-grown phenotypes from aba2 and wild type. This study will provide novel mechanisms by which ABA crosstalks to nutrient and salt stress signaling.