Gibberellic acid (GA), a ubiquitous phytohormone, has various effects on regulators of plant growth and development. GAs promote growth by overcoming growth restraint mediated by DELLA proteins (DELLAs). DELLAs, in the GRAS family of plant-specific nuclear proteins, are nuclear transcriptional regulators harboring a unique N-terminal GA perception region for binding the GA receptor GIBBERELLIN INSENSITIVE DWARF1 (GID1) and a C-terminal GRAS domain necessary for GA repression activity via interaction with multiple regulatory proteins. The N-terminal conserved region of DELLAs evolved to form a mode of GID1/DELLA-mediated GA signaling originating in bryophytes and ferns. Binding of GA to GID1 increases the affinity between DELLAs and a SCF E3 ubiquitin-ligase complex, thus promoting the eventual destruction of DELLAs by the 26S proteasome. DELLAs negatively regulate GA response by releasing transcription factors to directly activate downstream genes and indirectly regulate GA biosynthesis genes increasing GA responsiveness and feedback control by promoting GID1 transcription. GA communicates extensively with other plant hormones and uses crosstalk to regulate plant growth and development. In this review, we summarize current understanding of evolutionary DELLA-mediated gibberellin signaling and functional diversification of DELLA, focusing primarily on interactions of DELLAs with diverse phytohormones.

With the increasing promotion of simplified rapeseed cultivation in recent years, the development of cultivars with high resistance to herbicides is urgently needed. We previously developed M342, which shows sulfonylurea herbicide resistance, by targeting acetohydroxyacid synthase (AHAS), a key enzyme in branched-chain amino acid synthesis. In the present study, we used a progeny line derived from M342 for an additional round of ethyl methane sulfonate mutagenesis, yielding the novel mutant DS3, which harbored two mutations in AHAS genes and showed high sulfonylurea resistance. One mutation was the substitution Trp574Leu, as in M342, according to Arabidopsis protein sequencing. The other site was a newly recognized substitution, Pro197Leu. A KASP marker targeting Pro197Leu was developed and reliably predicted the response to sulfonylurea herbicides in the F₂ population. The combination of Trp574Leu and Pro197Leu in DS3 produced a synergistic effect that greatly increased herbicide resistance. Analysis of the protein structures of AHAS1 and AHAS3 in wild-type and single-gene mutant plants revealed three-dimensional protein conformational changes that could account for differences in herbicide resistance characteristics including toxicity tolerance, AHAS enzyme activity, and AHAS gene expression.