Abstract
MYB transcription factors are involved in many biological processes, including metabolism, development and responses to biotic and abiotic stresses. RADIALIS-LIKE SANT/MYB 1 (RSM1) belongs to a MYB-related subfamily, and previous transcriptome analysis suggests that RSM1 may play roles in plant development, stress responses and plant hormone signaling. However, the molecular mechanisms of RSM1 action in response to abiotic stresses remain obscure. We show that down-regulation or up-regulation of RSM1 expression alters the sensitivity of seed germination and cotyledon greening to abscisic acid (ABA), NaCl and mannitol in Arabidopsis. The expression of RSM1 is dynamically regulated by ABA and NaCl. Transcription factors ELONGATED HYPOCOTYL 5 (HY5) and HY5 HOMOLOG (HYH) regulate RSM1 expression via binding to the RSM1 promoter. Genetic analyses reveal that RSM1 mediates multiple functions of HY5 in responses of seed germination, post-germination development to ABA and abiotic stresses, and seedling tolerance to salinity. Pull-down and BiFC assays show that RSM1 interacts with HY5/HYH in vitro and in vivo. RSM1 and HY5/HYH may function as a regulatory module in responses to ABA and abiotic stresses. RSM1 binds to the promoter of ABA INSENSITIVE 5 (ABI5), thereby regulating its expression, while RSM1 interaction also stimulates HY5 binding to the ABI5 promoter. However, no evidence was found in the dual-luciferase transient expression assay to support that RSM enhances the activation of ABI5 expression by HY. In summary, HY5/HYH and RSM1 may converge on the ABI5 promoter and independently or somehow dependently regulate ABI5 expression and ABI5-downstream ABA and abiotic stress-responsive genes, thereby improving the adaption of plants to the environment.
Highlights
Plants grow in a continuously changing environment that imposes various stresses
We show that a MYB-related transcription factor, RADIALIS-LIKE SANT/MYB 1 (RSM1), plays important roles in abscisic acid (ABA) and salinity signaling in Arabidopsis, and we dissect the relationship between RSM1 and HYPOCOTYL 5 (HY5)
The Chromatin immunoprecipitation (ChIP) assays confirmed that RSM1 associated with fragment B, but not with the control sequence (ACTIN2) or fragment A, in vivo (Fig 4E). These findings demonstrate that RSM1 may function as a transcription factor by binding to the ABA INSENSITIVE 5 (ABI5) promoter to regulate ABI5 expression and influence the ABA signaling pathway
Summary
Plants grow in a continuously changing environment that imposes various stresses Abiotic stresses such as drought and salinity are amongst these environmental stresses [1, 2]. In the PYR/ PYLs/RCARs-initiated core ABA signaling pathway, PYR/PYLs interact with and inhibit clade-A PP2Cs, including ABI1, ABI2, HAB1 and PP2CA/AHG3 [9, 10]. These PP2Cs negatively regulate ABA responses [7] by de-phosphorylating and inhibiting positive regulators of ABA signaling, e.g. a subfamily of ABA-activated SNF1-related protein kinases 2 (SnRK2s) including SnRK2.2, SnRK2.3 and SnRK2.6 in Arabidopsis [11]. The ABFs bind to ABA-responsive promoter elements (ABRE) to induce the expression of ABA-inducible genes and thereby control seed germination and seedling development [5]
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