Brassinosteroids (BRs) play an essential role in promoting skotomorphogenesis, yet the underlying mechanisms remain unknown. Here we report that a plant-specific BLISTER (BLI) protein functions as a positive regulator of both BR signaling and skotomorphogenesis in Arabidopsis (Arabidopsis thaliana). We found that the glycogen synthase kinase 3 (GSK3)-like kinase BRASSINOSTEROID INSENSITIVE2 (BIN2) interacts with and phosphorylates BLI at four phosphorylation sites (Ser70, Ser146, Thr256 and Ser267) for degradation; in turn, BR inhibits degradation of BLI. Specifically, BLI cooperates with the BRASSINAZOLE RESISTANT1 (BZR1) transcription factor to facilitate the transcriptional activation of BR-responsive genes. Genetic analyses indicated that BLI is essentially required for BZR1-mediated hypocotyl elongation in the dark. Intriguingly, we reveal that BLI and BZR1 orchestrate the transcriptional expression of gibberellin (GA) biosynthetic genes to promote the production of bioactive GAs. Our results demonstrate that BLI acts as an essential regulator of Arabidopsis skotomorphogenesis through promoting BR signaling and GA biosynthesis.

Grain weight is a major determinant of wheat (Triticum aestivum L.) yield and is controlled by quantitative trait loci (QTLs) derived from natural variations. Here, we report the cloning of a major yield QTL in bread wheat that functions in the chlorophyll biosynthesis pathway. We found that the natural variation of CHELATASE SUBUNIT I-A (CHLI-A), encoding a magnesium chelatase subunit, enhances chlorophyll content and photosynthesis rate, leading to increased leaf area and grain weight. Increasing CHLI-A expression increases grain weight, indicating that photosynthesis is a limiting factor of wheat yield potential. The CHLI-A gene is absent in a portion of elite varieties, suggesting the potential of using this gene to improve grain yield in wheat.