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2 Acta Physiologiae Plantarum

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ABA and GA signaling pathways interact and regulate seed germination and seedling development under salt stress

100%

Yuan K. , Rashotte A. M. , Wysocka-Diller J. W.

Acta Physiologiae Plantarum

2011

tom 33

nr 2

Soil salinity is one of the most significant abiotic stresses limiting plant growth. The ability of plant cells to adapt and survive under salt stress conditions involves triggering a network of signaling events including hormones such as abscisic acid (ABA) known to regulate many important aspects of growth and development. ABA is also known to play a critical role in stress responses such as the regulation of seed germination under salt and osmotic stress. Components of the gibberellic acid (GA) signaling pathway have also been shown to regulate germination; however, the involvement of GA signaling in salt and osmotic stress is largely unexamined. Here, we examined the responses of mutants in the GA signaling pathway (rgl2 and spy) and in the ABA signaling pathway (abi3 and abi5) to salt (NaCl) and osmotic (mannitol) stress during seed germination and early seedling development. Several mutants show resistance to increased levels of both salt and osmotic stress at germination and later stages of seedling development suggesting a role for ABA and GA signaling in these processes. qRT-PCR was employed to determine the effect of salt stress on seed germination via transcriptional control of the components in GA or ABA signaling pathways. We found that RGL2, ABI3, and ABI5 transcripts are greatly induced by NaCl in wildtype plants, but show little if any induction by NaCl in mutant backgrounds suggesting that this regulation of induction during salt stress may occur through ABA–GA crosstalk. Overall, our results indicate that each of the ABA and GA signaling pathways is individually involved in regulation of various seedling developmental stages under stress conditions. In addition, these two hormone pathways appear to be interacting in the regulation of germination and early seedling growth under salt and osmotic stress conditions.

Two NAC transcription factors from Citrullus colocynthis, CcNAC1, CcNAC2 implicated in multiple stress responses

100%

Wang Z. , Rashotte A. M. , Moss Z. G. , Dane F.

nr 03

NAC (no apical meristem, Arabidopsis transcription activation factor 1 and 2, cup-shaped cotyledon 2) transcription factors (TFs) play important roles in plant growth, development, and responses to abiotic and biotic stress. Two novel NAC TFs were isolated from Citrullus colocynthis, a highly drought-tolerant cucurbit species: CcNAC1 and CcNAC2 each with conserved A–E NAC domains. Subcellular location of CcNAC1 and CcNAC2 investigated via transient expression of 35S::CcNAC1: :GFP and 35S::CcNAC2::GFP fusion constructs in Arabidopsis protoplasts, revealed nuclear localization. The transactivation ability of CcNACs was examined in the GAL4 yeast assay system, and showed that only the C-terminal domain of CcNAC1 has the ability to activate reporter genes LacZ and His3. The CcNAC genes accumulated in a tissue-specific manner with expression levels in male flowers of C. colocynthis higher than leaves, hypocotyls or roots. Genome walking was used to isolate the CcNAC1 and CcNAC2-promoter regions. A high number of stress-related sequence motifs were detected, especially in the CcNAC1 promoter. C. colocynthis seedlings were treated with PEG, abscisic acid, salicylic acid (SA), jasmonic acid (JA), H₂O₂, ethylene, gibberellic acid (GA), wounding or salt. High CcNAC1 expression levels were detected following JA application, and wounding, while high CcNAC2 levels followed treatment with GA, JA, SA, and wounding, indicative of differential regulation of these stress responsive TFs in this cucurbit species.