Abstract
The circadian clock regulates numerous biological processes in plants, especially development and stress responses. CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) is one of the core components of the day–night rhythm response and is reportedly associated with ambient temperature in Arabidopsis thaliana. However, it remains unknown if alternative splicing of ZmCCA1 is modulated by external stress in maize, such as drought stress and photoperiod. Here, we identified three ZmCCA1 splice variants in the tropical maize line CML288, which are predicted to encode three different protein isoforms, i.e., ZmCCA1.1, ZmCCA1.2, and ZmCCA1.3, which all retain the MYB domain. In maize, the expression levels of ZmCCA1 splice variants were influenced by photoperiod, tissue type, and drought stress. In transgenic A. thaliana, ZmCCA1.1 may be more effective than ZmCCA1.3 in increasing drought tolerance while ZmCCA1.2 may have only a small effect on tolerance to drought stress. Additionally, although CCA1 genes have been found in many plant species, alternative CCA1 splicing events are known to occur in species-specific ways. Our study provides new sight to explore the function of ZmCCA1 splice variants’ response to abiotic stress, and clarify the linkage between circadian clock and environmental stress in maize.
Highlights
Subtropical and tropical maize lines have been used as germplasm to improve maize quality and yield compared with temperate maize lines due to their abundant genetic variations
The circadian clock is involved in photoperiod-mediated flowering and accurately perceives external input signals to generate endogenous rhythmic outputs during an approximate 24 h cycle, which can be synchronized with the environment by regulating key basic metabolic processes including photosynthesis, hypocotyl elongation, and floral transition [3]
ZmCCA1.1 consisted of a 2157 bp open reading frame (ORF) encoding a protein of 718 amino acids with a molecular weight of 78.2 kDa, a pI of 6.08, more than 147 bp 50untranslated region (UTR), and 282 bp 30UTR, whereas ZmCCA1.2 and ZmCCA1.3 were found to encode proteins of 676 and 709 amino acids with 249 and 87 bp 30UTR, respectively
Summary
Subtropical and tropical maize lines have been used as germplasm to improve maize quality and yield compared with temperate maize lines due to their abundant genetic variations. The circadian clock is involved in photoperiod-mediated flowering and accurately perceives external input signals to generate endogenous rhythmic outputs during an approximate 24 h cycle, which can be synchronized with the environment by regulating key basic metabolic processes including photosynthesis, hypocotyl elongation, and floral transition [3]. The transcriptional regulation and molecular functions of circadian clock genes have been studied in Arabidopsis thaliana, including CCA1 [6], LATE ELONGATED HYPOCOTYL (LHY) [7], TIMING OF CAB EXPRESSION 1 (TOC1), and GIGANTEA (GI). Feedback loops mediated by CCA1, LHY, and TOC1 constitute one of the circadian clock regulatory models whereby CCA1 and LHY can bind directly to the TOC1 promoter as the transcriptional repressors that suppress TOC1 accumulation. The molecular mechanisms of the circadian clock gene in maize are yet to be reported; cloning of these associated genes will provide a theoretical foundation for understanding the maize circadian clock
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