The transgenic A. thaliana of the gene PIIN_00131 from the root endophytic fungus Serendipita indica shows early flowering

Serendipita indica possesses the ability to improve plant growth, enhance the quality of produced crops, alleviate various environmental stresses. Our previous research showed that S. indica promotes early flowering and increases plant growth. However, the molecular mechanism underlying this effect remains elusive. Therefore, transgenic Arabidopsis thaliana lines expressing the gene PIIN_00131 from S. indica were constructed in this study. The results showed a notable increase in the numbers of rosette leaves, above-ground fresh weight and plant height. The flowering time was accelerated by 6–7 days, compared to the control. It was found that the transgenic Arabidopsis lines showed significantly elevated expression levels of genes related to the flowering photoperiodic pathway (such as PHYA, CRY1, and CO), gibberellin pathway (such as GA3), and flower formation-related genes (such as FT and AP1). The levels of GA1 and trans-zeatin in transgenic lines showed a significant increase, while the levels of ABA, JA, SA, and ACC significantly decreased. Furthermore, the Arabidopsis proteins, ATP-dependent protease (FIB16.1) involved in proteolysis, was identified to interact with PIIN_00131 by yeast two-hybrid technology. The protein PIIN_00131 interacts with the protein FIB16.1 to cause changes in hormones and flowering genes in Arabidopsis, resulting in early flowering. This research will deepen our understanding of the mechanisms by which S. indica induces early flowering in plants.