Short-chain chlorinated paraffins (SCCPs) were added to Annex A of the Stockholm Convention on Persistent Organic Pollutants in April, 2017. As a consequence of this regulation, increasing production and usage of alternatives, such as medium- and long-chain chlorinated paraffins (MCCPs and LCCPs, respectively), is expected. Little is known about the environmental fate and behavior of MCCPs and LCCPs. In the present study, SCCPs, MCCPs, and LCCPs were analyzed in nine wildlife species from paddy fields in the Yangtze River Delta, China, using atmospheric pressure chemical ionization-quadrupole time-of-flight mass spectrometry. SCCPs, MCCPs, and LCCPs were detected in all samples at concentrations ranging from <91-43 000, 96-33 000, and 14-10 000 ng/g lipid, respectively. Most species contained primarily MCCPs (on average 44%), with the exception of collared scops owl and common cuckoo, in which SCCPs (43%) accumulated to a significantly (i.e., p < 0.05) greater extent than MCCPs (40%). Cl groups were dominant in most species except for yellow weasel and short-tailed mamushi, which contained primarily Cl groups. Principal components analysis, together with CP concentrations and carbon stable isotope analysis showed that habitat and feeding habits were key factors driving CP accumulation and congener group patterns in wildlife. This is the first report of LCCP exposure in wildlife and highlights the need for data on risks associated with CP usage.

Strigolactones (SLs) are a group of carotenoid-derived small molecules synthesized by plants. As a special class of plant hormones, SLs regulate shoot branching [1-7]. Intriguingly, SLs are also exuded into the soil as rhizospheric signals for communication with arbuscular mycorrhizal fungi (AMF) [8] and seeds of root parasitic weeds [9-11]: SLs facilitate AMF symbiosis with a wide range of land plants, which improves nutrient and water uptake of the host plants [1], and stimulate germination of the seeds of root parasitic weeds such as Striga for parasitic growth on host plants, which causes agricultural disaster with the loss of billions of dollars' worth of crops every year [9]. Previous studies have identified several key components in the SL signaling pathway. In model plant Arabidopsis, the F-box protein MAX2 (MORE AXILLARY GROWTH2) regulates both SL-repressed shoot branching and karrikin-induced seed germination [12, 13]; however, the α/β hydrolase D14 (DWARF14) regulates shoot branching but not seed germination [14], the repressor proteins SMXL6/7/8 (SMAX1-LIKE family) function in shoot branching [15, 16], while SMAX1 (SUPPRESSOR OF MAX2 1) regulates seed germination [17]. Most recently, we have defined D14 as a non-canonical hormone receptor that mediates the hydrolysis of SL to a covalently linked intermediate molecule (CLIM), which serves as the active form of SL that covalently engages the interior of D14 thus effecting plant branching suppression [18]. Studies on SL perception by parasitic weeds remain challenging due to the genetic intractability of the phenotypes and the obligate parasitic property of the experimental system [9]. A group of α/β hydrolase ShHTLs/ ShKAI2s (Striga hermonthica HYPO-SENSITIVE TO LIGHT/KARRIKIN INSENSITIVE2 proteins), which are paralogs of D14, were uncovered to hydrolyze SL and mediate the SL-induced seed germination [9-11]. These ShHTLs, including the most active ShHTL7, were proposed to act as the SL receptor in Striga hermonthica [9-11]. However, the active form of SL perceived by

Seeds of the root parasitic plant Striga hermonthica can sense very low concentrations of strigolactones (SLs) exuded from host roots. The S. hermonthica hyposensitive to light (ShHTL) proteins are putative SL receptors, among which ShHTL7 reportedly confers sensitivity to picomolar levels of SL when expressed in Arabidopsis thaliana. However, the molecular mechanism underlying ShHTL7 sensitivity is unknown. Here we determined the ShHTL7 crystal structure and quantified its interactions with various SLs and key interacting proteins. We established that ShHTL7 has an active-site pocket with broad-spectrum response to different SLs and moderate affinity. However, in contrast to other ShHTLs, we observed particularly high affinity of ShHTL7 for F-box protein AtMAX2. Furthermore, ShHTL7 interacted with AtMAX2 and with transcriptional regulator AtSMAX1 in response to nanomolar SL concentration. ShHTL7 mutagenesis analyses identified surface residues that contribute to its high-affinity binding to AtMAX2 and residues in the ligand binding pocket that confer broad-spectrum response to SLs with various structures. Crucially, yeast-three hybrid experiments showed that AtMAX2 confers responsiveness of the ShHTL7–AtSMAX1 interaction to picomolar levels of SL in line with the previously reported physiological sensitivity. These findings highlight the key role of SL-induced MAX2–ShHTL7–SMAX1 complex formation in determining the sensitivity to SL. Moreover, these data suggest a strategy to screen for compounds that could promote suicidal seed germination at physiologically relevant levels.