miRNA-targeted auxin nuclear signalling elements orchestrate flower fate and drought response in yellow lupine.

Yellow lupine (Lupinus luteus L.) is a promising protein crop, but domestication has increased flower abscission. Flowers in higher whorls are more likely to abscise, providing a model to study factors influencing flower fate before abscission zone formation. We hypothesise that auxin localisation and miRNA-modulated signal transduction orchestrate flower development and abscission, particularly under drought. We investigated the indole-3-acetic acid (IAA) distribution in ovules and tested the effects of IAA, NPA (auxin transport inhibitor), and PCIB (auxin signalling blocker) on flower retention. Bioinformatic analyses of transcriptome data profiled miRNA-regulated auxin pathway elements (TIR1/AFBs, ARFs), with domain structures analysed for functional divergence. Selected miRNA-mRNA modules were analysed for their role in inflorescence drought response. IAA accumulation exhibited slight differences in upper pre-anthesis flowers. In the field experiment, PCIB treatment led to increased retention of generative organs, suggesting the vital role of auxin nuclear signalling in flower fate. Bioinformatic analyses identified miRNAs (MIR393, MIR160, MIR167, one novel) regulating TIR1/AFB and ARF6,8,17,18. qPCR revealed the differential expression of AFB3-, ARF6-, and ARF18-encoding transcripts and corresponding miR393, miR167, and miR160 during flower development and drought stress. However, miRNA-target expression lacked a strictly negative correlation, indicating other regulating players.