David C. Nelson
（Department of Botany & Plant Sciences, University of California, Riverside, USA）
Negative-feedback mechanisms that limit the perception of karrikins and an unknown plant hormone
Karrikins (KAR) are plant growth regulators found in smoke that putatively function as analogs of an undiscovered plant hormone, KAI2 ligand (KL). Karrikins probably are metabolized by plants into a bioactive signal prior to perception by KARRIKIN INSENSITIVE2 (KAI2), an a/b-hydrolase and receptor. Upon activation by KAR/KL, KAI2 associates with the F-box protein MAX2 and the transcriptional corepressors SMAX1 and SMAX1-LIKE2 (SMXL2). This results in polyubiquitination and degradation of SMAX1 and SMXL2, and the initiation of downstream transcriptional responses that regulate germination, seedling photomorphogenesis, root hair growth, several drought tolerance traits, and symbiotic associations with arbuscular mycorrhizal fungi. In this seminar, I will present two recently discovered negative-feedback mechanisms that limit activation of the KAR/KL signaling pathway through complementary modes of action. The first mechanism involves KARRIKIN UPREGULATED F-BOX1 (KUF1), a positive transcriptional marker of KAR/KL signaling. Our genetic analysis strongly suggests that KUF1 inhibits the metabolism of KAR and KL. We have now identified a family of proteins that likely are targeted for polyubiquitination by KUF1 and degraded. The second mechanism involves D14-LIKE2 (DLK2), a homolog of KAI2 and the strigolactone receptor DWARF14(D14)/DECREASED APICAL DOMINANCE2(DAD2). DLK2 proteins maintain the characteristic catalytic triad of a/b-hydrolases but lack the highly conserved residues of KAI2 and D14 that mediate interaction with MAX2. Our data currently support a role for DLK2 in catabolism of KL.
（School of Biology, University of Leeds, UK）
Underground, Overground: Understanding How Plants Coordinate Shoot Growth with Soil Resources
Plants must carefully regulate their growth according to the availability of resources in the environment. To do this, they can use both direct stimuli that provide information about resource availability in the present, but also indirect stimuli that provide them with information about potential resource availability in the future. In this talk, I discuss how plants are able to use the presence of neighbouring root systems as indirect stimuli to help optimise their shoot growth relative to future resource availability. I will discuss the mechanisms by which plants are able to detect their neighbours, and our progress identifying the signals that communicate this information. I will also discuss how shoot systems are able to use this information to coordinate their growth and reproductive development to maximise reproductive success. Finally, I will discuss the application of this information to understanding crop-weed interactions, as a specific example of underground plant-plant interactions.