探索臺大選NTU036兔眼藍莓的表型和開花基因表達及其對溫度之反應

Abstract

近年來世界各國藍莓（Vaccinium spp.）的需求量不斷提升。短日照（short day, SD）和低溫是誘導藍莓花芽分化的兩個環境因子。然而，有關藍莓開花的分子機制尚未完全闡明。兔眼藍莓雜交子代‘NTU-15-036-RR’(‘Bonita’ x ‘Climax’) (以下稱為‘036’)在臺灣的亞熱帶氣候下具有不開花的特性，此外，‘036’還具有極度矮小的樹冠。在本文第一個實驗中，將‘Climax’作為對照組，與‘036’盆植植株，自2023年9月至2024年1月，置於三種不同溫度的自然光人工氣候室中（30/25°C、25/20°C和20/15°C），評估對其營養生長和生殖生長的影響。 結果顯示，‘036’在兩個較高溫度的處理下，植株維持不開花及其矮性性狀，但在20/15°C的涼溫中，11月下旬之前枝條明顯伸長。相對地，‘Climax’在25/20°C和20/15°C的溫度下枝條生長較佳；至處理結束，僅有置於20/15°C 的’036’植株開花。結果顯示，’036’之營養生長及開花可能對高溫敏感，因而在臺灣的亞熱帶氣候下，植株矮化且無法開花。 在本文第二個實驗中，於處理期間採樣並分析FT（FLOWERING LOCUS T，重要的開花相關基因）和COL5（CONSTANCE-LIKE 5，與光周期性相關基因）的基因表達量。於處理後一個月，20/15°C 中的‘036’FT表達較‘Climax’高。處理後兩個月 (11月底)，‘Climax’在30/25°C和20/15°C的FT表達顯著增高，之後於1月3日，25/20°C中的植株也有顯著的增加。於處理期間，‘036’在涼溫處理下之FT表達量上升的時間點早於‘Climax’，符合其後續開花之表現，但隨後下降並保持較低表達量。總體而言，‘036’的FT表達量在試驗期間內多較‘Climax’低，可以與‘036’在臺灣亞熱帶氣候下不開花有關。 兩個品種在三個溫度處理下的COL5基因表達量皆沒有差異，顯示試驗期間的光周期並未影響‘036’開花特性。 本實驗結果說明，‘036’的營養生長及開花對溫度敏感，且FT 基因表達在高溫下受抑制，是而在臺灣的亞熱帶氣候下表現出矮化及不開花的特性。

The demand for blueberries (Vaccinium spp.) has increased globally in recent years. It is well-known that the floral initiation-induction in blueberries is triggered by two environmental signals: short day length (SD) and cool temperature. However, the molecular mechanisms involved in blueberries’ flowering are not fully elucidated. ‘NTU-15-036-RR’ (hereafter called ‘036’), a rabbiteye blueberry (V. virgatum Aiton) selected from a ‘Bonita’ x ‘Climax’ population in the National Taiwan University blueberry breeding program, was investigated for its non-flowering nature under the subtropical climate in Taiwan. In addition, ‘036’ possesses an extreme dwarfness. In the first experiment, ‘Climax’, as a control, and ‘036’ were subjected to three different temperature treatments (30/25°C, 25/20°C, and 20/15°C) from September 2023 to January 2024, and their vegetative and reproductive growth were evaluated. The results showed that the shoot growth of ‘036’ maintained its dwarfness in the two warm temperature treatments but was more active in the 20/15°C treatment until late November. On the other hand, shoot growth of ‘Climax’ was normal in the two warm temperature rooms but slow in the cool room. No plant produced flowers during the experimental period except ‘036’ in 20/15°C, suggesting that sensitivity to heat might be the cause of dwarfness and non-flowering in ‘036’ under the warm subtropical climate. In the second experiment, the expression levels of FLOWERING LOCUS T (FT), an important flowering-related gene, and CONSTANCE Like 5 (COL 5), a key gene involved in photoperiodicity were measured at several time points during experimental period. On November 1st, FT expression was lower in ‘Climax’ than in ‘036’ in all temperature treatments. On November 30th, FT expression in ‘Climax’ was significantly high at 30/25°C and 20/15°C and increased continuously until early January at 25/20°C. The results indicated that the onset timing of FT expression increase in ‘036’ was earlier than in ‘Climax’ in the cool temperature treatment, coinciding with its consequent flowering. Nevertheless, the expression of FT was overall lower in ‘036’ than in ‘Climax’ in all treatments. The expression levels of COL5 were not different between both cultivars and among all temperature treatments during the experimental period, suggesting that the photoperiodic flowering pathway didn’t affect the flowering trait of ‘036’. In conclusion, the results suggested that vegetative growth and flowering of ‘036’ could be promoted by cool temperature that encourages FT expression.