Gene promoters are key elements that regulate gene expression, and exist in constitutive, tissue-specific, and inducible forms (Li et al., 2006). The Arabidopsis rd29A promoter is induced in response to adverse conditions (Yamaguchi SK and Shinozaki K, 1994), and comprises one abscisic acid (ABA)-responsive cis-acting element (ABRE) sequence, two DNA replication-related elements (DREs), and two DRE-related CCGAC sequences (Seki et al., 2002). The total length of the promoter is 1446 bp; however, responses to drought, high salinity, and low temperature stress are regulated by the region between base pairs − 174 to -55(Jin et al, 2020). rd29A, also known as LTI78 and COR78, carries three introns at the same position as those in rd29B (Horvath et al., 1993). Evidence suggests that retention of the DRE element within the rd29A promoter enables rapid induction of the rd29A gene under conditions of high salinity, drought, or low temperature stress, indicating that the rapid expression of this gene does not depend on the action of intracellular ABA. In addition to Arabidopsis, the inducible rd29A promoter has been reported in tobacco and wheat (Gao et al., 2005). Furthermore, the GUS reporter gene has been experimentally introduced into potatoes, and GUS activity has been detected in transgenic potato plants under stress conditions (Zhang et al., 2005). Research using transgenic plants has commonly utilized the constitutive 35S promoter; however, the constitutive expression of downstream genes often leads to slow plant growth(Li et al, 2006). As rd29A is a stress-inducible promoter, the expression of downstream genes is only increased in the presence of external stress. Thus, when the stress is removed, gene expression will cease, which preserve the plant’s resources and does not impact growth.
Fluorescent proteins have wide applications and play important roles in biological research involving live cell imaging and analyses of protein expression. mCherry encodes a red fluorescent protein, which was originally extracted from mushroom coral, and can be used as a marker to track target molecules and cellular components. Compared with green fluorescent protein (GFP), mCherry has longer excitation and emission wavelengths and is not affected by the chlorophyll autofluorescence of green tissues (Li et al., 2012). Therefore, it can also be used with GFP without the risk of cross-reaction. Transgene-free progeny were easily obtained via mCherry fluorescence screening in our previous study(Ouyang et al, 2020). In this study, we investigated the application of mCherry, a fluorescent protein, to evaluate the inducible promoter rd29A in Arabidopsis under low temperature. The use of mCherry as a reporter gene can aid identification of the expression efficiency of the promoter.