Abstract
Abscisic acid (ABA) plays important roles in many aspects of plant growth and development, and responses to diverse stresses. Although much progress has been made in understanding the molecular mechanisms of ABA homoeostasis and signaling, the mechanism by which plant cells integrate ABA trafficking and signaling to regulate plant developmental processes is poorly understood. In this study, we used Arabidopsis STOMATAL CYTOKINESIS DEFECTIVE 2/RIPENING-REGULATED PROTEIN 1 (SCD2/RRP1) mutants and overexpression plants, in combination with transcriptome and protein-interaction assays, to investigate SCD2/RRP1 involvement in the integration of ABA trafficking and signaling in seed germination and seedling growth. Manipulation of SCD2/RRP1 expression affected ABA sensitivity in seed germination and seedling growth, as well as transcription of several ABA transporter genes and ABA content. RNA-sequencing analysis of Arabidopsis transgenic mutants suggested that SCD2/RRP1 was associated with ABA signaling via a type 2C protein phosphatase (PP2C) protein. The N- and C-terminal regions of SCD2/RRP1 separately interacted with both PYRABACTIN RESISTANCE 1 (PYR1) and ABA INSENSITIVE 1 (ABI1) on the plasma membrane, and SCD2/RRP1 acted genetically upstream of ABI1. Interestingly, ABA inhibited the interaction of SCD2/RRP1 with ABI1, but did not affect the interaction of SCD2/RRP1 with PYR1. These results suggested that in Arabidopsis SCD2/RRP1participates in early seed development and growth potentially through clathrin-mediated endocytosis- and clathrin-coated vesicle-mediated ABA trafficking and signaling. These findings provide insight into the mechanism by which cells regulate plant developmental processes through ABA.
Highlights
During the lifetime of higher plants, the primary nutrient organs such as roots, stems, and leaves grow first for survival, followed by reproductive organs such as flowers, fruits, and seeds for sexual reproduction in response to diverse internal and external cues
These results demonstrated that alteration of Arabidopsis STOMATAL CYTOKINESIS DEFECTIVE 2 (SCD2)/RRP1 expression affected plant growth
Induced 1), JA (JAZ1, 2, 3, 5, 6, 9, and 10: Jasmonate ZIMdomain 1, 2, 3, 5, 6, 9, and 10; MYC2: myelocytomatosis protein 2, a basic helix-loop-helix Leu zipper transcription factor), cytokinin (ARR15: two-component type-A response regulator), and salicylic acid (PR1: pathogenesis-related protein 1; Figure 4). The majority of these differentially expressed genes (DEGs) were upregulated in the OE plants and downregulated in the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) plants in comparison with the WT (Figure 4). Given that these transgenic plants showed no response to JA in seed germination and seedling growth, these results suggested that SCD2/RRP1 might be involved in Abscisic acid (ABA) signaling through the ABA INSENSITIVE 1 (ABI1) protein, which is a crucial negative regulator of ABA signaling
Summary
During the lifetime of higher plants, the primary nutrient organs such as roots, stems, and leaves grow first for survival, followed by reproductive organs such as flowers, fruits, and seeds for sexual reproduction in response to diverse internal and external cues. Abscisic acid (ABA), a growth inhibitor identified in the early 1960s (Liu and Carnsdagger, 1961; Ohkuma et al, 1963), plays important roles in a variety of plant growth and developmental processes, including seed maturation and dormancy, seed germination, seedling and root growth, floral transition, fruit ripening, and stomatal movement, and participates in the adaptive responses of plants to biotic and abiotic stresses, including drought, high salinity, chilling, and pathogen attack (Leung and Giraudat, 1998; Finkelstein et al, 2002; Himmelbach et al, 2003; Cutler et al, 2010; Zhang, 2014) These physiological responses are triggered by endogenous ABA contents, which are tightly controlled by ABA biosynthesis, catabolism, and transport (Nambara and Marion-Poll, 2005; Umezawa et al, 2006; Boursiac et al, 2013; Kuromori et al, 2018). These diverse subcellular enzymes associated with ABA homoeostasis suggest the presence of ABA in different subcellular compartments, which is consistent with the multiple functions of ABA in plants in response to developmental and environmental cues (Xu et al, 2013)
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