RNA-Seq recently revealed candidate genes regulating specific biological processes in triploid loquat such as the gibberellin-induced fruit setting pathway, fruit development and ripening, and low-temperature stress response. It enables rapid gene discovery and creates more sensitive and accurate transcriptome profiles than other techniques.
RNA-Seq technology comprehensively identifies transcripts and facilitates transcriptome analysis. However, the mechanisms regulating loquat bud differentiation and flowering time are poorly understood.
In Shanghai, China, loquat flower bud differentiation occurs between July and September followed by blooming from early October to January of the following year. Bud initiation may require special environmental conditions such as high temperature and moderate drought stress. The loquat flower bud may persist for several months. Loquat floral buds are usually derived from vegetative buds on shoots produced mainly during summer. It blooms in autumn and forms terminal panicles in early winter. Loquat ( Eriobotrya japonica Lindl.) (Rosaceae) is a subtropical evergreen fruit tree native to China. To date, however, little is known about the mechanism by which ABA promotes loquat bud differentiation or the ABA-associated regulatory pathway that controls loquat flowering time. The ABA content dramatically rises in loquat apical buds and strongly influences loquat flower bud induction and differentiation. In loquat, however, ABA plays a positive role in flower bud formation. ABA is generally considered a flowering suppressor. Previous studies have demonstrated phytohormone crosstalk in flower induction. Flowering time is affected by environmental conditions and phytohormones. FT and FT-like play pivotal roles in the flowering of fruit trees in the Rosaceae family such as apple, pear, peach, and loquat. FLOWERING LOCUS T (FT) is a crucial mobile signal. Photoperiod as well as circadian, ambient temperature, vernalization, autonomous, gibberellin, and aging pathways are implicated. Several major pathways in Arabidopsis include floral integrator genes that govern flowering time. Flower bud differentiation and, by extension, flowering itself, are influenced by sophisticated regulatory networks. It involves elegant mechanisms that integrate complex signals including photoperiod and temperature. Flowering has evolved to maximize outcrossing and mitigate the damaging effects of frost. Understanding the mechanisms that control flowering events is essential for efficient fruit reproduction. The results of the present study help clarify gene transcription during loquat flowering.įlowering is the onset of plant reproduction and an important phenophase. Thus, ABA is vital in regulating floral bud formation in loquat. The ABA:IAA ratio sharply rose and attained a peak during bud differentiation. However, the ABA content was about ten-fold higher in the apical buds of ‘Baiyu’ than in those of ‘Huoju’. There was no significant difference between ‘Baiyu’ and ‘Huoju’ in terms of IAA content. Hence, they might regulate loquat flowering time. Moreover, transcripts of the ABA 8′-hydroxylases ( EjABH2, EjABH4, and EjABH4-like2), the ABA receptors ( EjPYL4/8), and the bZIP transcription factor EjABI5-like were upregulated in ‘Baiyu’ compared with ‘Huoju’. Compared with those in ‘Huoju’, EjFT, EjFY, EjFLK, and EjCAL1-like were significantly upregulated in ‘Baiyu’.
Of these, 42 DETs controlled flowering time while 17 other DETs were associated with the ABA signaling pathway. A total of 28,842 differentially expressed transcripts (DETs) were identified. To identify candidate genes regulating flowering time in loquat, we used RNA-Seq technology to conduct a comparative transcriptome analysis of differentiating apical buds collected from the early-flowering variety ‘Baiyu’ and the late-flowering variety ‘Huoju’. Flowering is an important phenophase of plant species, however, knowledge about the regulatory mechanism controlling flowering cues in loquat is limited.
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