BIL9 Promotes Both Plant Growth via BR Signaling and Drought Stress Resistance by Binding with the Transcription Factor HDG11.

Drought stress is a major threat leading to global plant and crop losses in the context of the climate change crisis. Brassinosteroids (BRs) are plant steroid hormones, and the BR signaling mechanism in plant development has been well elucidated. Nevertheless, the specific mechanisms of BR signaling in drought stress are still unclear. Here, we identify a novel Arabidopsis gene, BRZ INSENSITIVE LONG HYPOCOTYL 9 (BIL9), which promotes plant growth via BR signaling. Overexpression of BIL9 enhances drought and mannitol stress resistance and increases the expression of drought-responsive genes. BIL9 protein is induced by dehydration and interacts with the HD-Zip IV transcription factor HOMEODOMAIN GLABROUS 11 (HDG11), which is known to promote plant resistance to drought stress, in vitro and in vivo. BIL9 enhanced the transcriptional activity of HDG11 for drought-stress-resistant genes. BIL9 is a novel BR signaling factor that enhances both plant growth and plant drought resistance.

Substituted Phthalimide AC94377 Is a Selective Agonist of the Gibberellin Receptor GID1.

Gibberellin (GA) is a major plant hormone that regulates plant growth and development and is widely used as a plant growth regulator in agricultural production. There is an increasing demand for function-limited GA mimics due to the limitations on the agronomical application of GA to crops, including GA's high cost of producing and its leading to the crops' lodging. AC94377, a substituted phthalimide, is a chemical that mimics the growth-regulating activity of GAs in various plants, despite its structural difference. Although AC94377 is widely studied in many weeds and crops, its mode of action as a GA mimic is largely unknown. In this study, we confirmed that AC94377 displays GA-like activities in Arabidopsis (Arabidopsis thaliana) and demonstrated that AC94377 binds to the Arabidopsis GIBBERELLIN INSENSITIVE DWARF1 (GID1) receptor (AtGID1), forms the AtGID1-AC94377-DELLA complex, and induces the degradation of DELLA protein. Our results also indicated that AC94377 is selective for a specific subtype among three AtGID1s and that the selectivity of AC94377 is attributable to a single residue at the entrance to the hydrophobic pocket of GID1. We conclude that AC94377 is a GID1 agonist with selectivity for a specific subtype of GID1, which could be further developed and used as a function-limited regulator of plant growth in both basic study and agriculture.

Brassinosteroid-related transcription factor BIL1/BZR1 increases plant resistance to insect feeding.

The plant steroid hormones brassinosteroids (BRs) play important roles in plant growth and responses to stresses. The up-regulation of pathogen resistance by BR signaling has been analyzed, but the relationship between BR and insect herbivores remains largely unclear. BIL1/BZR1 is a BR master transcription factor known to be involved in the regulation of plant development through work conducted on a gain of function mutation. Here, we analyzed the function of BIL1/BZR1 in response to insect feeding and demonstrated that resistance against thrip feeding was increased in the bil1-1D/bzr1-1D mutant compared to wild-type. We generated Lotus japonicus transgenic plants that over-express the Arabidopsis bil1/bzr1 mutant, Lj-bil1/bzr1-OX. The Lj-bil1/bzr1-OX plants showed increased resistance to thrip feeding. The expression levels of the jasmoninc acid (JA)-inducible VSP genes were increased in both Arabidopsis bil1-1D/bzr1-1D mutants and L. japonicus Lj-bil1/bzr1-OX plants. The resistance to thrip feeding caused by the BIL1/BZR1 gene may involve JA signaling.

Genome editing in plants using CRISPR type I-D nuclease.

Genome editing in plants has advanced greatly by applying the clustered regularly interspaced short palindromic repeats (CRISPRs)-Cas system, especially CRISPR-Cas9. However, CRISPR type I-the most abundant CRISPR system in bacteria-has not been exploited for plant genome modification. In type I CRISPR-Cas systems, e.g., type I-E, Cas3 nucleases degrade the target DNA in mammals. Here, we present a type I-D (TiD) CRISPR-Cas genome editing system in plants. TiD lacks the Cas3 nuclease domain; instead, Cas10d is the functional nuclease in vivo. TiD was active in targeted mutagenesis of tomato genomic DNA. The mutations generated by TiD differed from those of CRISPR/Cas9; both bi-directional long-range deletions and short indels mutations were detected in tomato cells. Furthermore, TiD can be used to efficiently generate bi-allelic mutant plants in the first generation. These findings indicate that TiD is a unique CRISPR system that can be used for genome engineering in plants.