BZR1 Physically Interacts with SPL9 to Regulate the Vegetative Phase Change and Cell Elongation in Arabidopsis.

Lingyan Wang,Min Fan,Yanfei Hu,Ming-Yi Bai,Jinyang Lyu,Chao Han,Ping Yu

doi:10.3390/ijms221910415

Lingyan Wang, Min Fan + Show 5 more

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https://doi.org/10.3390/ijms221910415

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Abstract

As sessile organisms, the precise development phase transitions are very important for the success of plant adaptability, survival and reproduction. The transition from juvenile to the adult phase—referred to as the vegetative phase change—is significantly influenced by numbers of endogenous and environmental signals. Here, we showed that brassinosteroid (BR), a major growth-promoting steroid hormone, positively regulates the vegetative phase change in Arabidopsis thaliana. The BR-deficient mutant det2-1 and BR-insensitive mutant bri1-301 displayed the increased ratio of leaf width to length and reduced blade base angle. The plant specific transcription factors SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) are key masters for the vegetative phase transition in plants. The expression levels of SPL9, SPL10 and SPL15 were significantly induced by BR treatment, but reduced in bri1-116 mutant compared to wild-type plants. The gain-of-function pSPL9:rSPL9 transgenic plants displayed the BR hypersensitivity on hypocotyl elongation and partially suppressed the delayed vegetative phase change of det2-1 and bri1-301. Furthermore, we showed that BRASSINAZOLE-RESISTANT 1 (BZR1), the master transcription factor of BR signaling pathway, interacted with SPL9 to cooperatively regulate the expression of downstream genes. Our findings reveal an important role for BRs in promoting vegetative phase transition through regulating the activity of SPL9 at transcriptional and post-transcriptional levels.

Highlights

The transition from the juvenile to adult stage is referred to as the vegetative phase change and is crucial for the reproductive success and survival of higher plants [1]
BRASSINAZOLE-RESISTANT 1 (BZR1) contains the amino-terminal DNA binding domain, PEST domain, which is responsible for the interaction with PHOSPHATASE 2A (PP2A), and the carboxy-terminal domain, which itself is critical for the association with BRASSINOSTEROID INSENSITIVE2 (BIN2)
To confirm the interaction between BZR1 and SPL9, protein-protein pull down assay was performed using purified proteins fused glutathione S transferase (GST) or maltose binding protein (MBP) expressed from Escherichia coli

Summary

Introduction

The transition from the juvenile to adult stage is referred to as the vegetative phase change and is crucial for the reproductive success and survival of higher plants [1]. The microRNA 156 (miR156) and its target transcription factors SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) are the main regulatory factors of the vegetative phase transition in plants [4,5]. A wide range of signals, including sugar, gibberellin acid (GA), abscisic acid (ABA), auxin and endogenous epigenetic factors, regulate the activity of the miR156-SPL module to modulate the vegetative phase change [3,6,7,8]. Overexpression of miR156 target mimic, MIM156, which produces an mRNA binding to miR156, inhibits the activity of miR156 and increases the transcript levels of SPLs (such as SPL3, SPL4, SPL5, SPL9, and SPL15), shortening the juvenile phase [9,10,19,20]. Our recent study further showed that gibberellin inhibited the formation of axillary buds in Arabidopsis by promoting the degradation of DELLA proteins to release their inhibiting effects on the transcriptional activity of SPL9 [30]

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