Abstract
Numerous CCT genes are known to regulate various biological processes, such as circadian rhythm regulation, flowering, light signaling, plant development, and stress resistance. The CCT gene family has been characterized in many plants but remains unknown in the major cereal wheat (Triticum aestivum L.). Extended exposure to low temperature (vernalization) is necessary for winter wheat to flower successfully. VERNALIZATION2 (VRN2), a specific CCT-containing gene, has been proved to be strongly associated with vernalization in winter wheat. Mutation of all VRN2 copies in three subgenomes results in the eliminated demands of low temperature in flowering. However, no other CCT genes have been reported to be associated with vernalization to date. The present study screened CCT genes in the whole wheat genome, and preliminarily identified the vernalization related CCT genes through expression analysis. 127 CCT genes were identified in three subgenomes of common wheat through a hidden Markov model-based method. Based on multiple alignment, these genes were grouped into 40 gene clusters, including the duplicated gene clusters TaCMF6 and TaCMF8, each tandemly arranged near the telomere. The phylogenetic analysis classified these genes into eight groups. The transcriptome analysis using leaf tissues collected before, during, and after vernalization revealed 49 upregulated and 31 downregulated CCT genes during vernalization, further validated by quantitative real-time PCR. Among the differentially expressed and well-investigated CCT gene clusters analyzed in this study, TaCMF11, TaCO18, TaPRR95, TaCMF6, and TaCO16 were induced during vernalization but decreased immediately after vernalization, while TaCO1, TaCO15, TaCO2, TaCMF8, and TaPPD1 were stably suppressed during and after vernalization. These data imply that some vernalization related CCT genes other than VRN2 may exist in wheat. This study improves our understanding of CCT genes and provides a foundation for further research on CCT genes related to vernalization in wheat.
Highlights
Timing of flowering is a crucial agronomic trait that determines the environmental adaptability and grain yield in plants [1]
Based on the available genome-wide assembly and annotation of wheat cultivar Chinese Spring (CS) [43], wheat CCT genes were screened against their unique hidden Markov model (HMM) using the HMMER3.0 package
A total of 54 CO/COL genes, 46 CCT MOTIF FAMILY (CMF) genes, 15 PSEUDO-RESPONSE REGULATOR (PRR) genes, and 12 ZINC-FINGER PROTEIN EXPRESSED IN INFLORESCENCE MERISTEM (ZIM) genes belonging to 18 CO/COL clusters, 13 CMF clusters, 5 PRR clusters, and 4 ZIM clusters were identified in wheat
Summary
Timing of flowering is a crucial agronomic trait that determines the environmental adaptability and grain yield in plants [1]. Plants integrate exogenous signals, such as photoperiod and winter temperature (vernalization), and endogenous signals such as autonomous pathway to modulate flowering time [2]. The CCT domain, initially described in the Arabidopsis protein CONSTANS (CO), CONSTANS-LIKE (COL), and TIMING OF CAB EXPRESSION 1 (TOC1), is about 43 amino acids long and has a putative nuclear localization signal at the N-terminal [3]. The proteins with the CCT domain have been named as CCT proteins and divided into four subfamilies based on the additional domains. These four subfamilies are CCT MOTIF FAMILY (CMF), CO/COL, PSEUDO-RESPONSE REGULATOR (PRR), and ZINC-FINGER PROTEIN EXPRESSED IN INFLORESCENCE MERISTEM (ZIM). CMF proteins do not harbor any characterized domains other than the CCT domain; CO/COL proteins harbor one or two additional B-box domains; PRR proteins have Response_reg domain [4]; ZIM proteins, referred to as CMF proteins in some works, harbor three domains: tify, CCT, and ZnF_GATA [5,6,7,8]
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