DWARF14, A Receptor Covalently Linked with the Active Form of Strigolactones, Undergoes Strigolactone-Dependent Degradation in Rice.

Qingliang Hu,Jiayang Li,Mingjiang Chen,Guifu Liu,Yanhui Jing,Xiaoguang Song,Hong Yu,Lei Wang,Yajun He,Bing Wang,Simiao Liu,Liang Jiang,Xiangbing Meng

doi:10.3389/fpls.2017.01935

Abstract

Strigolactones (SLs) are the latest confirmed phytohormones that regulate shoot branching by inhibiting bud outgrowth in higher plants. Perception of SLs depends on a novel mechanism employing an enzyme-receptor DWARF14 (D14) that hydrolyzes SLs and becomes covalently modified. This stimulates the interaction between D14 and D3, leading to the ubiquitination and degradation of the transcriptional repressor protein D53. However, the regulation of SL perception in rice remains elusive. In this study, we provide evidences that D14 is ubiquitinated after SL treatment and degraded through the 26S proteasome system. The Lys280 site of the D14 amino acid sequence was important for SL-induced D14 degradation, but did not change the subcellular localization of D14 nor disturbed the interaction between D14 and D3, nor D53 degradation. Biochemical and genetic analysis indicated that the key amino acids in the catalytic center of D14 were essential for D14 degradation. We further showed that D14 degradation is dependent on D3 and is tightly correlated with protein levels of D53. These findings revealed that D14 degradation takes place following D53 degradation and functions as an important feedback regulation mechanism of SL perception in rice.

Highlights

Strigolactones (SLs), a group of carotenoid-derived terpenoid lactones produced by plants, were initially characterized as signals that enable parasitic plants to detect their host (Cook et al, 1966), and as signals recognized by arbuscular mycorrhizal (AM) fungi in the rhizosphere to build the symbiotic association with host plants (Akiyama et al, 2005)
We show that the hydrolase activity of D14 and the intact functions of D3 and D53 are both required for SL-induced D14 degradation
We examined the expression levels of D14 and D53 upon 5 μL sense primer (5 μM) rac-GR24 treatment in 2-week-old seedlings, and found that D14 transcripts were unaffected within 6 h treatment, while D53 transcripts were strongly induced after 2 h treatment (Figure 1B)

Summary

Introduction

Strigolactones (SLs), a group of carotenoid-derived terpenoid lactones produced by plants, were initially characterized as signals that enable parasitic plants to detect their host (Cook et al, 1966), and as signals recognized by arbuscular mycorrhizal (AM) fungi in the rhizosphere to build the symbiotic association with host plants (Akiyama et al, 2005). The key components required for SL biosynthesis and signaling have been identified from genetic characterizations of highly branched mutants, including ramosus (rms) in pea (Pisum sativum), more axillary growth (max) in Arabidopsis thaliana, decreased apical dominance (dad) in petunia (Petunia hybrida), and dwarf (d) or high-tillering dwarf (htd) in rice (Oryza sativa). In the SL biosynthetic pathway, SLs are derived from all-trans-β-carotene, which is converted to 9cis-β-carotene by the isomerase DWARF27 (D27) (Lin et al, 2009; Alder et al, 2012), and subsequently catalyzed into carlactone by carotenoid cleavage oxygenase 7 (CCD7) and CCD8 (Beveridge et al, 1996; Sorefan et al, 2003; Booker et al, 2004; Seto et al, 2014). A newly identified sulfotransferase LOW GERMINATION STIMULANT1 (LGS1) is responsible for a change of the dominant SL in root exudates from 5-deoxystrigol to orobanchol via an unknown mechanism and regulates the Striga resistance (Gobena et al, 2017)

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Conclusion