GSE96041
Chloroplast signalling gates thermotolerance in Arabidopsis
Temperature has a major role in plant growth and survival, for example wheat yields decrease by about 6% for every 1°C rise in global temperature [1]. High temperatures induce the expression of protective chaperones and modulate growth responses. Key players in the heat protection response are transcription factors of the HEAT SHOCK FACTOR A1 (HSFA1) family [2]. However the pathways that activate the HSFA1 class TFs, and how these perceive temperature and integrate it with other environmental signals are not clear. Plants are exposed to considerable diurnal temperature variation, and have evolved pathways to anticipate likely future conditions. For example, the cold response pathway is gated by the circadian clock, enabling the degree of responsiveness to cold to be controlled in the context of the environment [3, 4] and genes promoting elongation growth and flowering in response to warm temperature are induced during the night via thermosensory phytochromes [5 ,6]. It is not known in Arabidopsis if the warm temperature protective pathways are gated. In this study we find that there is strong diurnal variation in the heat stress response of Arabidopsis, and we show that this correlates with the expression of HSP70 in the day night cycle. The dark to light transition is in fact sufficient to robustly induce expression of warm temperature protective genes such as HSP70. A forward genetic screen with a HSP70-Luciferase reporter line revealed genes necessary for controlling this process and identified a central role for chloroplast signalling in the warm temperature response that accounts for diurnal variation in thermotolerance. Overall design: RNA-seq was generated in duplicate for an ss4 mutant and WT at 17°C, ss3/4, pgm, ss3/4/pgm at 17°C ZT0 and ZT2, and DCMU and DBMIB treated seedlings at 22°C and 27°C. A WT timecourse at 22°C and 27°C has a single replicate.