Abstract
Litchi is an important subtropical fruit tree that requires an appropriately low temperature to trigger floral initiation. Our previous studies have shown that reactive oxygen species (ROS) are involved in litchi flowering. To identify oxidative stress-induced flowering related genes in leaves, ‘Nuomici’ potted trees were grown at medium low-temperature conditions (18/13 °C for day/night, medium-temperature). The trees were treated with the ROS generator methyl viologen dichloride hydrate (MV) as the MV-generated ROS treatment (MM, medium-temperature plus MV) and water as the control treatment (M, medium-temperature plus water). Sixteen RNA-sequencing libraries were constructed, and each library generated more than 5,000,000 clean reads. A total of 517 differentially expressed genes (DEGs) were obtained. Among those DEGs, plant hormone biosynthesis and signal transduction genes, ROS-specific transcription factors, such as AP2/ERF and WRKY genes, stress response genes, and flowering-related genes FLOWERING LOCUS T1 (FT1) and FLOWERING LOCUS T2 (FT2) were significantly enriched. Then, as a confirmatory experiment, the potted trees were uniformly sprayed with MV, N,N’-dimethylthiourea (DMTU, ROS scavenger) plus MV, and water at medium-temperature. The results showed that the MV-generated ROS promoted flowering and changed related gene expression, but these effects were repressed by DMTU treatment. The results of our studies indicate that ROS could promote flowering and partly bypass chilling for litchi flowering.
Highlights
Litchi is an evergreen fruit tree commercially cultivated in southern Asia, South Africa, and Australia
Litchi trees grown under high-temperature conditions with only a few leaves treated with low temperature could still produce flowers, the panicles were small [4], suggesting that these low-temperature-treated leaves can produce flowering signals that could be transported to the apical meristem to activate flowering through the phloem
Treatment (M) produced no flowers with new flushes, whereas trees treated with reactive oxygen species (ROS) in combination with the ROS scavenger DMTU (MMD) produced considerably fewer flowers, the percentage of flowering trees was the same as with MV treatment (MM)
Summary
Litchi is an evergreen fruit tree commercially cultivated in southern Asia, South Africa, and Australia. In the model plant Arabidopsis, CONSTANS (CO) is regarded as a direct activator of FLOWERING LOCUS T (FT), and the FT protein is indicated to be a long-seeking florigen that migrated from leaves to the shoot apical meristem (SAM) to promote floral initiation [5,6]. In other plants such as cucurbit and rice, the FT protein or its analog is proven to be a long-distance florigenic signal transported in the phloem to the SAMs and to activate the transition from the vegetative meristem to the inflorescence meristem [7,8]. Two kinds of tissues may play important roles in
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