Strigolactones (SLs) act as an important class of phytohormones to regulate plant shoot branching, and also serve as rhizosphere signals to mediate interactions of host plants with soil microbes and parasitic weeds. SL receptors in dicots, such as DWARF14 in Arabidopsis (AtD14), RMS3 in pea, and ShHTL7 in Striga, serve as unconventional receptors that hydrolyze SLs into a D-ring-derived intermediate CLIM and irreversibly bind CLIM to trigger SL signal transduction. Here, we show that D14 from the monocot rice can complement Arabidopsis d14 mutant and interact with the SL signaling components in Arabidopsis. Our results further reveal that rice D14, similar to SL receptors in dicots, also serves as an unconventional hormone receptor that generates and irreversibly binds the active form of SLs. These findings uncover the conserved functions of D14 proteins in monocots and dicots.

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.

Simple β-lactones are potent irreversible antagonists for strigolactone receptors

Animals rely on nervous systems to cope with environmental variability, whereas plants are characterized by lack of nervous system but still have evolved systemic communication systems through signaling molecules that trigger long-distance defense signaling events when encountered with environmental challenges. Here, our genetic screening of the previously constructed hairpin RNA-based Arabidopsis library identifies a glutathione (GSH)-deficient mutant that has high accumulation of glutamate (Glu), a previously defined wound signal essential for activating plant defense, but disharmoniously exhibits attenuation of defense signaling events. We further uncover GSH as a critical signaling molecule that relies on GLUTAMATE RECEPTOR-LIKE 3.3 (GLR3.3) to trigger long-distance calcium-based defense signaling events in plants. Our findings offer new insights into highly sophisticated systemic defense systems evolved by plants to defend against herbivory and pathogen invasion.

Camellia sinensis ‘hainanensis’ (Hainan Sheng tea) is an endemic tea germplasm resource native to Hainan Island, China. Using complete chloroplast genome sequencing combined with comprehensive comparative analyses, we elucidated the genetic architecture of six C. sinensis accessions. The chloroplast genomes exhibited a typical quadripartite circular structure (~157 Kb) comprising 80 unique protein-coding genes, 30 tRNA genes, and 4 rRNA genes. Expansion and contraction of the inverted repeat (IR) regions led to boundary shifts affecting genes, while nucleotide diversity within the large single-copy (LSC) and small single-copy (SSC) regions (Pi > 0.0035) markedly exceeded that of the conserved IR regions. Phylogenetic reconstruction revealed that C. sinensis ‘hainanensis’ shared the closest evolutionary relationship with Yunnan large-leaf tea (Camellia grandibracteata), supporting its independent lineage within the genus. A polymorphic molecular marker derived from the hypervariable non-coding region (trnT–psbD) may serve as a useful preliminary marker for distinguishing C. sinensis ‘hainanensis’ from related taxa and hybrids. This study provides the first comprehensive comparison of complete chloroplast genomes of six C. sinensis ‘hainanensis’, identifies three distinct plastome types, and develops a molecular marker that can reliably distinguish these types, offering valuable genomic resources for future studies on tea evolution and germplasm identification.