Abstract
Thermomorphogenesis is the morphological response of plants to an elevation in the ambient temperature, which is mediated by the bHLH transcription factor PIF4. The evening-expressed clock component, PRR5, directly represses the expression of PIF4 mRNA. Additionally, PRR5 interacts with PIF4 protein and represses its transactivation activity, which in turn suppresses the thermoresponsive growth in the evening. Here, we found that the B-box zinc finger protein, BBX18, interacts with PRR5 through the B-Box2 domain. Deletion of the B-Box2 domain abolished the functions of BBX18, including the stimulation of PIF4 mRNA expression and hypocotyl growth. Overexpression of BBX18, and not of B-Box2-deleted BBX18, restored the expression of thermoresponsive genes in the evening. We further show that BBX18 prevents PRR5 from inhibiting PIF4-mediated high temperature responses. Taken together, our results suggest that BBX18 regulates thermoresponsive growth through the PRR5-PIF4 pathway.
Highlights
Plants adapt to high-temperature stresses in various ways, one of which is through morphological changes
These results indicate that overexpression of B-BOX 18 (BBX18) causes constitutive thermomorphogenic responses at normal temperatures
The levels of BBX18-YFP in BBX18-OX plants under the two growth temperatures were not significantly different (Figure 1C). These results show that the protein stability of BBX18 is not affected by the ambient temperature changes
Summary
Plants adapt to high-temperature stresses in various ways, one of which is through morphological changes. The morphological changes in response to elevated ambient temperatures are collectively called thermomorphogenesis (Quint et al, 2016; Casal and Balasubramanian, 2019). Thermomorphogenesis is characterized by elongated hypocotyls, petioles, and primary roots, and leaf hyponasty. These morphological alterations are likely to increase survival during heat stress, partly by enhancing leaf cooling capacity (Crawford et al, 2012). Thermomorphogenesis is an adaptive response that enables plants to mitigate the damages caused by high temperatures, it is an irreversible and energy intensive process. It is controlled by the integration of multiple environmental and endogenous signals, and ambient temperature
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