Exogenous Hormones Affect the Corm Expansion of Sagittaria trifolia in Hydroponic Conditions

The tip of the underground stolon of arrowhead (Sagittaria trifolia) can perceive rhizosphere mechanical resistance and promote corm expansion by regulating the biosynthesis and accumulation of plant hormones. However, corm development of S. trifolia is affected under hydroponic conditions with low mechanical resistance. This study aimed to promote the formation and expansion of S. trifolia corms under hydroponic conditions and explore its potential regulatory mechanism through exogenous hormone application and transcriptome analysis. Exogenous ABA, JA, and SA was applied to hydroponic S. trifolia, and the key candidate genes regulating corm expansion were identified by transcriptome assay. The results showed that both MeJA and ABA could promote the corm expansion under hydroponic conditions, while SA inhibited corm development at the early stage of treatment and induced a large number of stolons to emerge and branch from the underground part of S. trifolia at the later stage. Transcriptome analysis showed that the key genes related to ethylene, auxin and cytokinin, namely StriChr1G051240 (EIN3), StriChr3G133510 (EIN3), StriChr2G094080 (ARF), StriChr3G125830 (ARR), StriChr4G170530 (ARF), and StriChr5G184020 (ARF), were all differentially expressed in expanded S. trifolia corms that were induced by ABA treatment and high rhizosphere mechanical resistance. This finding indicated that ABA may act together with ethylene, auxin and cytokinin by regulating the expression of EIN3, ARR and ARF genes to promote the corm formation, in the condition of insufficient mechanical resistance. Current study provides a theoretical basis for elucidating the hormonal regulatory of S. trifolia corm expansion and improving the delayed corm expansion problem under hydroponic cultivation.