Life Science College, Northwest Normal University, Anning East Road 967, Anning, 730070 Lanzhou, Gansu, China.
Life Science College, Northwest Normal University, Anning East Road 967, Anning, 730070 Lanzhou, Gansu, China.
Plant Sci. 2021 Feb;303:110749. doi: 10.1016/j.plantsci.2020.110749. Epub 2020 Nov 24.
Photoperiod is a major determinant of chasmogamous (CH)-cleistogamous (CL) dimorphic flower development in Viola philippica, and only long-day (LD) conditions induce CL flowers. In this study, it was found that the active gibberellin (GA) content in CL floral buds was higher than in CH floral buds formed under short-day (SD) conditions, suggesting that the biosynthesis of active GAs is enhanced by a longer photoperiod and may be associated with dimorphic flower development. Thus, the next step was to molecularly characterize the key V. philippica GA synthesis genes GA 20-oxidase (VpGA20ox) and GA 3-oxidase (VpGA3ox). In terms of the expression of VpGA20ox and VpGA3ox, it was found that the active GAs could be upregulated in developing pistils under both LD and SD conditions to develop functional pistils, and GAs could also accumulate in the stamens under SD conditions. The anthers and the adjacent petals were well developed under SD conditions. In contrast, the above-mentioned floral organs displayed low GA contents under LD conditions and were poorly developed. Although the application of paclobutrazol, an inhibitor of GA synthesis, did not reverse CL development under LD conditions, exogenous GAs could partially trigger the transition from CH to CL flowers under relative SD conditions (≤12 h daylight). This was coupled with the downregulation of B-class MADS-box genes, thereby restraining stamen and petal development. Both VpGA20ox and VpGA3ox exhibited similar expression profiles with B-class MADS-box genes in the development of the stamens and petals. Therefore, in response to photoperiod, GA signaling could affect the expression of B-class homeotic genes and regulate dimorphic flower development in Viola. As a compensation for poorly-developed nectaries, anthers, and petals, filament elongation, style shortness, and inward bending could ensure self-pollination in CL flowers. This work provides new insights into the regulation of CH-CL floral development and the evolutionary significance of the formation of dimorphic flowers.
光周期是堇菜属植物异熟雌雄同熟（CH）-雌雄同熟（CL）二型花发育的主要决定因素，只有长日照（LD）条件才能诱导 CL 花。在这项研究中，发现 CL 花芽中的活性赤霉素（GA）含量高于短日照（SD）条件下形成的 CH 花芽，这表明较长的光周期增强了活性 GAs 的生物合成，这可能与二型花发育有关。因此，下一步是从分子水平上对关键的堇菜属植物 GA 合成基因 GA 20-氧化酶（VpGA20ox）和 GA 3-氧化酶（VpGA3ox）进行表征。在 VpGA20ox 和 VpGA3ox 的表达方面，发现在 LD 和 SD 条件下，发育中的雌蕊中活性 GAs 可以被上调以发育出功能性雌蕊，并且 GAs 也可以在 SD 条件下积累在雄蕊中。在 SD 条件下，花药和相邻的花瓣发育良好。相比之下，在 LD 条件下，上述花器官的 GA 含量较低，发育不良。尽管应用赤霉素合成抑制剂 paclobutrazol 并不能逆转 LD 条件下的 CL 发育，但外源性 GAs 可以在相对 SD 条件（≤12 小时光照）下部分触发从 CH 到 CL 花的转变。这与 B 类 MADS 盒基因的下调有关，从而抑制雄蕊和花瓣的发育。在雄蕊和花瓣的发育过程中，VpGA20ox 和 VpGA3ox 与 B 类 MADS 盒基因表现出相似的表达模式。因此，GA 信号可以响应光周期，影响 B 类同源异形基因的表达，调节堇菜属植物的二型花发育。作为对发育不良的蜜腺、花药和花瓣的补偿，花丝伸长、花柱缩短和向内弯曲可以确保 CL 花的自花授粉。这项工作为 CH-CL 花发育的调控以及二型花形成的进化意义提供了新的见解。
