Abstract
The availability of sufficient chilling during bud dormancy plays an important role in the subsequent yield and quality of apple fruit, whereas, insufficient chilling availability negatively impacts the apple production. The transcriptome profiling during bud dormancy release and initial fruit set under low and high chill conditions was performed using RNA-seq. The comparative high number of differentially expressed genes during bud break and fruit set under high chill condition indicates that chilling availability was associated with transcriptional reorganization. The comparative analysis reveals the differential expression of genes involved in phytohormone metabolism, particularly for Abscisic acid, gibberellic acid, ethylene, auxin and cytokinin. The expression of Dormancy Associated MADS-box, Flowering Locus C-like, Flowering Locus T-like and Terminal Flower 1-like genes was found to be modulated under differential chilling. The co-expression network analysis indentified two high chill specific modules that were found to be enriched for “post-embryonic development” GO terms. The network analysis also identified hub genes including Early flowering 7, RAF10, ZEP4 and F-box, which may be involved in regulating chilling-mediated dormancy release and fruit set. The results of transcriptome and co-expression network analysis indicate that chilling availability majorly regulates phytohormone-related pathways and post-embryonic development during bud break.
Highlights
Role of various plant growth regulators during bud dormancy establishment and its release has been evaluated in several studies[11]
Chemical induced bud dormancy was reported to be associated with regulation of ethylene response factors (ERF), which resulted in temporary induction of endogenous ethylene synthesis[15]
Among the auxin signaling genes, the expression of auxin influx carrier (Contig_28284, Contig_40573 and Contig_52010), auxin response factor[3] (Contig_13946, Contig_17203, Contig_18222 and Contig_21441) and auxin response factor6-like (Contig_33446 and Contig_38459) was found to be upregulated under low chill conditions (Fig. 3B). These results suggest that auxin metabolism is modulated by temperature, where low chill condition is associated with higher expression of auxin biosynthesis genes as well as genes involved in auxin response during silver tip and fruit set stages as compared to high chill conditions
Summary
Role of various plant growth regulators during bud dormancy establishment and its release has been evaluated in several studies[11]. It was reported that ethylene production in buds may lead to accumulation of ABA, and this observation was in accordance with studies on potato tubers[17]. Auxin is another hormone, which is known to be involved in dormancy induction and maintenance. Already developed paradormant floral buds gradually switch to endodormant state and remain dormant until they accumulate sufficient chilling units (CUs; temperature ≤7 °C for one h) during winter. Change in climatic conditions of North-Western Himalayas led to decreasing trend of low temperature during November to February months[19] This led to decrease in available CUs necessary for dormancy release in apple and other fruit trees[20]. The present study was aimed to identify the differentially expressed genes (DEGs) associated with bud dormancy and fruit set under differential chilling availability
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