Floral indeterminacy is mediated by a negative feedback loop

Scientists have been curious as to how the shoot meristem maintains two adjacent cell populations that respond oppositely to the same systemic flowering signal. In this study by Huang et al., the authors reveal that LEAFY (LFY) transcription factor directly binds to the DNA of TERMINAL FLOWER1 (TFL1) and regulates its expression. Using mutant studies and complementation, the authors reiterate that LFY promotes determinate branching, with lfy mutants losing the determinacy of flowers; by contrast,TFL1 maintains indeterminacy at the inflorescence meristem such that tfl1 mutants exhibit determinate shoots.  Through fluorescence in situ hybridization, the authors confirm that seasonal cues trigger florigen (FT) production and LFY up-regulation in the central region of all shoot meristems. Interestingly, they observe that within the inflorescence meristem, LFY forms a negative feedback loop with TFL1. The authors demonstrate that this loop buffers LFY levels to preserve the indeterminate growth in the inflorescence meristem. They also show that lateral meristems lack this buffering mechanism, causing determinacy. Using computational simulation modeling, the authors indicate that in these side branches, LFY prompts a fate switch, shifting the plant to producing flowers by triggering various floral genes, contradicting its buffering role that promotes indeterminacy in the inflorescence meristem. The authors also predict the likelihood of additional factor (s) that act directly or indirectly upon LFY. The authors conclude that at onset of strong flowering cue, shoot indeterminacy functions as a context-specific response thereby driving the shoot tip to grow indefinitely while the side branches produce flowers. (Summary by Sonal Sachdev sci3ntyst , sci3ntyst.bsky.social) Science 10.1126/science.adv5429