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Abstract
Seedling emergence in monocots depends mainly on mesocotyl elongation, requiring coordination between developmental signals and environmental stimuli. Strigolactones (SLs) and karrikins are butenolide compounds that regulate various developmental processes; both are able to negatively regulate rice (Oryza sativa) mesocotyl elongation in the dark. Here, we report that a karrikin signaling complex, DWARF14-LIKE (D14L)-DWARF3 (D3)-O. sativa SUPPRESSOR OF MAX2 1 (OsSMAX1) mediates the regulation of rice mesocotyl elongation in the dark. We demonstrate that D14L recognizes the karrikin signal and recruits the SCFD3 ubiquitin ligase for the ubiquitination and degradation of OsSMAX1, mirroring the SL-induced and D14- and D3-dependent ubiquitination and degradation of D53. Overexpression of OsSMAX1 promoted mesocotyl elongation in the dark, whereas knockout of OsSMAX1 suppressed the elongated-mesocotyl phenotypes of d14l and d3 OsSMAX1 localizes to the nucleus and interacts with TOPLESS-RELATED PROTEINs, regulating downstream gene expression. Moreover, we showed that the GR24 enantiomers GR245DS and GR24 ent-5DS specifically inhibit mesocotyl elongation and regulate downstream gene expression in a D14- and D14L-dependent manner, respectively. Our work revealed that karrikin and SL signaling play parallel and additive roles in modulating downstream gene expression and negatively regulating mesocotyl elongation in the dark.
Highlights
Seed germination and seedling establishment require the coordination of developmental programs in response to various environmental signals (Gommers andMonte, 2018)
DWARF 14-LIKE (D14L) acts parallel to and additively with DWARF 14 (D14) to regulate rice mesocotyl elongation in the dark Both the karrikin and SL signaling pathways are involved in the regulation of mesocotyl elongation in the dark, which requires the function of D14L and D14, respectively (Hu et al, 2010; Gutjahr et al, 2015b; Kameoka and Kyozuka, 2015)
The expression of the D14L, D14L2 and D14L3 genes increased in Ossmax1 but decreased in OsSMAX1m-OE (Supplemental Figure 16D-F). These results indicated that the D14L-DWARF 3 (D3)-OsSMAX1m expression vector 329 (OsSMAX1) complex might act additively in conjunction with the D14-D3-DWARF 53 (D53) complex to control the expression of downstream genes, such as the D14L, D14L2 and D14L3
Summary
Seed germination and seedling establishment require the coordination of developmental programs in response to various environmental signals (Gommers andMonte, 2018). Mesocotyl elongation reflects the coordination of cell elongation and cell division processes, which are regulated precisely by phytohormones that integrate developmental signals and environmental stimuli (Sawers et al, 2002). The phytohormones that promote rice mesocotyl elongation include auxin (Epel et al., 1992), brassinosteroids (BRs) (Yamamuro et al, 2000 ), cytokinins (Hu et al, 2014), ethylene (Xiong et al, 2017), and gibberellins (GAs) (Takahashi, 1972), whereas abscisic acid (ABA) (Takahashi, 1972), jasmonic acid (JA) (Riemann et al, 2003; Xiong et al, 2017) and strigolactones (SLs) (Hu et al, 2010) inhibit mesocotyl elongation. The interaction of SLs with cytokinins (Hu et al, 2014) and BRs in the regulation of dark-induced rice mesocotyl elongation (Sun et al, 2018) suggests that mesocotyl development is an excellent model for investigating the cross-talk between
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