The strigolactone receptor DWARF14 regulates flowering time in Arabidopsis

The impact of phytohormones on the number and quality of flowers in Crocus sativus

BACKGROUND

Phytohormones play pivotal roles in regulating floral development and secondary metabolite synthesis in saffron (Crocus sativus L.).

RESULTS

This study investigated the effects of gibberellin (GA), abscisic acid (ABA), cytokinin (CK), and strigolactone (SL) on floral differentiation, stigma quality, crocin yield, and endogenous hormonal dynamics. GA significantly accelerated floral bud differentiation and apical bud elongation during reproductive transition, increasing flower number by 23.5% compared to the control. While CK also enhanced flowering (17.6% increase), ABA and SL showed milder effects. Intriguingly, ABA treatment markedly elevated crocin content, boosting crocin 1 and 2 levels by 49.5% and 99.2%, respectively, and total crocin yield per corm by 1.7-fold-the highest among all treatments. Endogenous hormone levels were dynamically regulated, with GA and ABA treatments upregulating endogenous ABA. However, qRT-PCR analysis revealed downregulated expression of ABA biosynthesis genes (ZEP and NCED) under GA and ABA treatments.

CONCLUSIONS

These findings highlight GA as the most effective hormone for increasing flower number and ABA as the optimal choice for enhancing crocin content. This study provides actionable insights for hormone-mediated agronomic strategies to simultaneously improve saffron's ornamental and medicinal value.

CYP722A1-mediated 16-hydroxylation of carlactonoic acid regulates the floral transition in Arabidopsis

Strigolactones (SLs) are multifunctional plant hormones and rhizosphere signals with diverse structures, roughly classified into two categories: canonical and noncanonical SLs. In Arabidopsis thaliana, SL biosynthesis mutants exhibit increased shoot branching and early flowering, underscoring their roles in developmental regulation. Shoot branching inhibition in Arabidopsis is associated with the methylation of a noncanonical SL, carlactonoic acid (CLA), catalyzed by CLA methyltransferase (CLAMT). Canonical SLs primarily function as rhizosphere signals, with their biosynthesis in dicots mediated by CYP722C enzymes. It is hypothesized that Arabidopsis does not produce canonical SL because of the lack of the CYP722C genes in its genome. Instead, Arabidopsis possesses CYP722A1, a member of the previously uncharacterized CYP722A subfamily, distinct from the CYP722C subfamily. This study demonstrates that Arabidopsis cyp722a1 mutants exhibit an earlier floral transition without excessive shoot branching. Biochemical analysis revealed that CYP722A1 catalyzes the hydroxylation of CLA to produce 16-hydroxy-CLA (16-HO-CLA), which is subsequently methylated by CLAMT to form 16-HO-MeCLA. 16-HO-CLA and 16-HO-MeCLA were detected in the wildtype; however, these compounds were absent in max1-4 mutant, deficient in CLA synthesis, and in cyp722a1 mutant. These findings show CYP722A1-dependent 16-hydroxylation activity of CLA in Arabidopsis. Moreover, they suggest that hydroxylated CLA specifically regulates floral transition, distinct from branching inhibition. Through the identification of CYP722A1 affecting floral transition, which is the distinct role of the CYP722A subfamily, this work provides insights into the structural diversification of SLs for specialized biological functions in plant development.

Arabidopsis RGLG1/2 regulate flowering time under different soil moisture conditions by affecting the protein stability of TOE1/2

Drought constitutes a significant environmental factor influencing the growth and development of plants. Consequently, terrestrial plants have evolved a range of strategies to mitigate the adverse effects of soil water deficit. One such strategy, known as drought escape, involves the acceleration of flowering under drought, thereby enabling plants to complete their life cycle rapidly. However, the molecular mechanisms underlying this adaptive response remain largely unclear. Using genetic, molecular, and biochemical techniques, we demonstrated that the AP2 family proteins TARGET OF EAT 1/2 (TOE1/2) are essential for the drought escape response in Arabidopsis, with a significant reduction in their protein stability observed during this process. Our findings indicate that the RING-type E3 ubiquitin ligases RING DOMAIN LIGASE 1/2 (RGLG1/2) interact with TOE1/2 and facilitate their degradation within the nucleus. Under water deficit conditions, there is increased expression of RGLG1/2, and their protein products translocate to the nucleus to ubiquitinate and degrade TOE1/2, thereby enhancing the drought escape response. Furthermore, the loss of TOE1/2 in drought conditions directly results in a reduction of drought resistance in plants, suggesting that drought escape is a high-risk behaviour for plants and that the RGLG1/2-TOE1/2 signalling cascade may serve as a central regulatory mechanism governing the trade-off between drought escape and drought tolerance in plants.