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ABA signalling promotes cell totipotency in the shoot apex of germinating embryos.

ABSTRACT: Somatic embryogenesis (SE) is a type of induced cell totipotency where embryos develop from vegetative tissues of the plant instead of from gamete fusion after fertilization. SE can be induced in vitro by exposing explants to growth regulators, such as the auxinic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The plant hormone abscisic acid (ABA) has been proposed to be a downstream signalling component at the intersection between 2,4-D- and stress-induced SE, but it is not known how these pathways interact to induce cell totipotency. Here we show that 2,4-D-induced SE from the shoot apex of germinating Arabidopsis thaliana seeds is characterized by transcriptional maintenance of an ABA-dependent seed maturation pathway. Molecular-genetic analysis of Arabidopsis mutants revealed a role for ABA in promoting SE at three different levels: ABA biosynthesis, ABA receptor complex signalling, and ABA-mediated transcription, with essential roles for the ABSCISIC ACID INSENSITIVE 3 (ABI3) and ABI4 transcription factors. Our data suggest that the ability of mature Arabidopsis embryos to maintain the ABA seed maturation environment is an important first step in establishing competence for auxin-induced cell totipotency. This finding provides further support for the role of ABA in directing processes other than abiotic stress response.

SUBMITTER: Chen B

PROVIDER: S-EPMC8483786 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:To address the lack of information on the function of CBC in the ABA signaling pathway during seed germination in barley, we employed TILLING to identify mutants of the genes hvcbp20.ab and hvcbp80.b and subsequently created the double mutant hvcbp20.ab/hvcbp80.b. We found that mutations in both CBC subunits resulted in a unique ABA response that differed from that of single mutants. Through transcriptomic analyses, we identified differential gene expression and alternative splicing patterns. Notably, the hvcbp20.ab/hvcbp80.b double mutant exhibited altered AS regulation and significant changes in brassinosteroid signaling following ABA exposure. Seeds were sterilized in 20% sodium hypochlorite solution for 20 min and washed with sterilized water for 5 min. They were then placed in Petri dishes with three layers of filters and treated with either sterilized water or sterilized water containing 75 μM ABA (cis-trans-abscisic acid; catalog no. 862169; Sigma-Aldrich). The seeds were stratified for 4 d at 4°C and then transferred to a growth chamber. Germination was defined as the visible emergence of the radicle through the seed coat and was assessed on 1 and 7 DAI (Days After Imbibition). The assay was performed in three biological replicates, each comprising 30 seeds of each genotype per petri dish. At 1 DAI, the embryos were isolated from the endosperm using a sharp scalpel blade, placed in microcentrifuge tubes (Eppendorf) containing RNAlater reagent, and stored at 4°C until RNA isolation. RNA was isolated using the mirVana™ Isolation Kit (Ambion, USA) following the manufacturer’s instructions. RNA was isolated in four biological replicates, each consisting of 20 embryos. In total, 32 RNA samples were extracted. RNA concentration and quality were assessed using a NanoDrop spectrophotometer (NanoDrop Technologies, Wilmington, USA) and Agilent Bioanalyzer (Agilent Technologies, Santa Clara, USA). We used grains and embryos of barley TILLING mutants: the hvcbp20.ab, in the CBP20 gene (CAP-BINDING PROTEIN 20; BaRT2v18chr6HG306340; 41,42), and hvcbp80.b, in the CBP80 gene (CAP-BINDING PROTEIN 80; BaRT2v18chr4HG195950), single mutants, the hvcbp20.ab/hvcbp80.b double mutant, and the 'Sebastian' wild-type (WT), all sourced from the HorTILLUS population 91. Single mutants were identified through TILLING in the M2 generation (then backcrossed with WT to clean the genetic background), and the double mutant was isolated from the F2 progeny following crossbreeding of the single mutants

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ABA signalling promotes cell totipotency in the shoot apex of germinating embryos.

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