Warm temperature modifies lineage cell fates to reduce stomata production in Arabidopsis

Stomatal abundance decrease in Arabidopsis triggered by warm-temperature is attributed to PIF4-mediated repression of SPEECHLESS (SPCH) expression. We identified the unknown developmental and transcriptional basis of this adaptive response. We analyzed stomatal lineage progression at warm- and control-T combining live-cell imaging and lineage-cell tracing with epidermal phenotyping, genetics and transcriptomics. Warm-T or PIF4 overexpression caused a fraction of stomatal precursors to lose their identity and become diverted, explaining stomatal index reduction, and hinting at developmental mechanisms underlying lineage progression. Triggering diverted precursor fate required extended exposure to warm-T, below which the process is reversible and stomatal index remains unchanged. Despite heat-induced gene reprogramming silenced key positive drivers of stomatal development as SPCH and MUTE, most lineages progressed and formed stomata. Transcriptomics revealed that warm-T shifted lineages towards uncommitted cell stages, which regained committed fates during recovery at control temperature. This indicates that stomatal development under changing temperatures occurs through partly rewired gene circuits involving alternative pathways. We used short 28ºC pulse treatments to analyze the transcriptional basis of stomatal lineage progression under warm temperature. All treatments began with Col-0 seedlings grown for 3 days at 21ºC (T0). Seedlings were then exposed to control (21ºC) or warm temperature (28ºC) for 16h (T1) and 24h (T2), or grown at 28°C for 16h and shifted back to 21°C for the following 8h (recovery treatment; Recov). RNA-seq data were obtained from three independent biological replicates per time-point and temperature, each consisting of 50 seedlings.