Abstract
Strigolactones (SLs) and related butenolides, originally identified as active seed germination stimulants of parasitic weeds, play important roles in many aspects of plant development. Two members of the D14 α/β hydrolase protein family, DWARF14 (D14) and KARRIKIN INSENSITIVE2 (KAI2) are essential for SL/butenolide signaling. The third member of the family in Arabidopsis, DWARF 14-LIKE2 (DLK2) is structurally very similar to D14 and KAI2, but its function is unknown. We demonstrated that DLK2 does not bind nor hydrolyze natural (+)5-deoxystrigol [(+)5DS], and weakly hydrolyzes non-natural strigolactone (-)5DS. A detailed genetic analysis revealed that DLK2 does not affect SL responses and can regulate seedling photomorphogenesis. DLK2 is upregulated in the dark dependent upon KAI2 and PHYTOCHROME INTERACTING FACTORS (PIFs), indicating that DLK2 might function in light signaling pathways. In addition, unlike its paralog proteins, DLK2 is not subject to rac-GR24-induced degradation, suggesting that DLK2 acts independently of MORE AXILLARY GROWTH2 (MAX2); however, regulation of DLK2 transcription is mostly accomplished through MAX2. In conclusion, these data suggest that DLK2 represents a divergent member of the DWARF14 family.
Highlights
Butenolides are lactone-containing heterocyclic molecules with important biochemical and physiological roles in plant life
The SL precursor carlactone is transported through the xylem and biologically active SLs are formed by MAX1 and its homologs (Seto et al, 2014; Zhang Y. et al, 2014; Al-Babili and Bouwmeester, 2015) and LATERAL BRANCHING OXIDOREDUCTASE (LBO; Brewer et al, 2016)
The predicted structure of DLK2 was compared with crystal structures of AtD14 and KARRIKIN INSENSITIVE2 (KAI2) (Figures 1B,C) using the I-TASSER server
Summary
Butenolides are lactone-containing heterocyclic molecules with important biochemical and physiological roles in plant life. Previously recognized as secondary metabolites, some types of butenolides were recently classified as plant hormones (Gomez-Roldan et al, 2008; Umehara et al, 2008). It has since become evident that SLs are involved in controlling a wide range of plant developmental processes, including root architecture, establishment of mycorrhiza, stature and shoot branching, seedling growth, senescence, leaf morphology and cambial activity (Snowden et al, 2005; Comprehensive Analysis of DWARF14-LIKE2 (DLK2). The SL precursor carlactone is transported through the xylem and biologically active SLs are formed by MAX1 and its homologs (Seto et al, 2014; Zhang Y. et al, 2014; Al-Babili and Bouwmeester, 2015) and LATERAL BRANCHING OXIDOREDUCTASE (LBO; Brewer et al, 2016). The subsequent signaling events are largely unknown, but tentatively the mechanism is similar to other systems employing targeted protein degradation (Smith and Li, 2014; Wallner et al, 2016)
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