Shade‐Induced <i>BnPRE1</i> – <i>BnGASA1</i> Transcriptional Cascade Facilitates Hypocotyl Elongation and Lodging in Rapeseed ( <i>Brassica napus</i> L.)

Lodging is a major cause of yield reduction in Brassica napus (B. napus). The primary factor that contributes to plant lodging is believed to be shade-induced hypocotyl/stem elongation. However, the precise mechanisms underlying this phenomenon in B. napus remain incompletely understood. We investigated the regulatory relationship between shade cues, hypocotyl elongation and lodging in this study. Combining GWAS, RNA-seq and genetic analyses, we identified BnGASA1 as a positive regulator of hypocotyl elongation and lodging of B. napus under shade conditions. Shade treatments activate the expression of BnGASA1. CRISPR-generated Bngasa1 mutants showed impaired shade response and lodging, while overexpression of BnGASA1 promoted hypocotyl elongation and lodging. Additionally, we observed that the hap_0 of BnC06.GASA1 is the dominant haplotype that negatively affects shade-induced hypocotyl elongation and lodging, but positively impacts yield improvement. Furthermore, we discovered that shade-induced activation of BnGASA1 was dependent on both BnPRE1 and BnPIF5. BnPIF5 directly binds to the promoter of BnPRE1 to activate its expression under shade conditions, resulting in the transcription of BnGASA1. As a result, both Bnpif5 and Bnpre1 mutants exhibited phenotypes resistant to lodging when grown under shade conditions. Our findings provide evidence of a direct correlation between shade-induced hypocotyl elongation and lodging, identify BnGASA1 as a novel regulator of hypocotyl elongation and lodging through GWAS, and demonstrate that shade cues activate the expression of BnGASA1 through the BnPIF5-BnPRE1 transcription cascade to promote lodging in B. napus.