The ubiquitin receptor StDA1 negatively regulates aurantio-obtusin biosynthesis by mediating the degradation of the StHDR1 protein in Senna tora seeds

Aurantio-obtusin is one of the major active components in Senna tora (S. tora) seeds. Although the ubiquitin receptor DA1 regulates plant seed size, it remains unclear if StDA1 regulates the accumulation of aurantio-obtusin in S. tora seeds. In this study, StDA1 is identified as a negative regulator of aurantio-obtusin production in S. tora seeds. Antisense overexpression of StDA1 led to larger seeds in S. tora and promoted the accumulation of aurantio-obtusin. In contrast, overexpression of StDA1 resulted in a decrease in aurantio-obtusin accumulation in seeds. Moreover, using StDA1 as a bait protein, we identified as an interacting factor, StHDR1, a key enzyme in the aurantio-obtusin biosynthesis pathway. StHDR1 is able to positively regulate aurantio-obtusin accumulation in S. tora seeds, which is the opposite effect of StDA1. Through its interaction with StHDR1, StDA1 promotes StHDR1 degradation via the 26S proteasome, thereby reducing the accumulation of aurantio-obtusin. In conclusion, StDA1 is a regulator that plays a role in the accumulation of aurantio-obtusin in S.tora seeds by modulating the stability of the StHDR1 protein. This discovery points to the StDA1-StHDR1 complex as a key regulatory node that could potentially be targeted to enhance the accumulation of aurantio-obtusin in S. tora seeds.