ELUCIDATING THE MOLECULAR MECHANISMS OF THE TEMPERATURE SHORT-TERM MEMORY IN ARABIDOPSIS PLANTS

GERMÁN MURCIA; CRISTINA NIETO; ROMINA SELLARO; SALOMÉ PRAT; JORGE CASAL

Congreso; LVIII Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research; 2022

Plants modify their growth in response to temperature. Warm temperatures enhance stem growth, while cold temperatures inhibit it. This environmental cue is sensed by three plant thermosensors identified so far: PHYTOCHROME B (phyB), PHYTOCHROME INTERACTING FACTOR 7 (PIF7) and EARLY FLOWERING 3 (ELF3). The photo-sensory receptor phyB, represses the activity of CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1). In turn, COP1 represses the activity of the growth repressor ELONGATED HYPOCOTYL 5 (HY5). Warm temperatures inhibit this pathway to promote growth. Also, elevated temperatures induce changes in the RNA hairpin present at the 5´-untranslated region of the transcription factor PIF7, increasing its translation. High levels of PIF7 protein promote stem growth. ELF3, a component of the evening complex, represses the expression of PHYTOCHROME INTERACTING FACTOR 4 (PIF4), encoding a protein that promotes stem growth. In turn, warmth decreases the activity of ELF3 via a process that exhibit liquid-liquid phase separation, increasing the levels of PIF4 to enhance growth. In nature, plants experience fluctuating temperatures. Thus, we wanted to investigate the molecular mechanisms that store information about daytime temperatures to control stem growth during the night. We observed that daytime temperatures affected the nighttime growth of the stem (hypocotyl). We analyzed the molecular dynamics of the key components of the signaling network and hypocotyl growth in mutants under different day/night temperatures. The short-term growth memory required ELF3, PIF4, COP1, and HY5, which carried daytime temperature information into the night. In response to increasing temperatures, ELF3 forms nuclear condensates associated with reduced activity. However, these nuclear speckles showed poor sensitivity to subsequent cooling, representing a typical hysteretic effect. PIF4, controlled by ELF3, followed the same pattern. We conclude that ELF3 achieves hysteresis and drives the PIF4 promoter into the same behavior, enabling a short-term memory of daytime temperature conditions.