Program in Molecular Plant Sciences, Washington State University, Pullman, WA, 99164, USA.
Department Crop and Soil Sciences, Washington State University, Pullman, WA, 99164, USA.
BMC Plant Biol. 2020 Dec 11;20(1):559. doi: 10.1186/s12870-020-02733-5.
The 29-member Arabidopsis AHL gene family is classified into three main classes based on nucleotide and protein sequence evolutionary differences. These differences include the presence or absence of introns, type and/or number of conserved AT-hook and PPC domains. AHL gene family members are divided into two phylogenetic clades, Clade-A and Clade-B. A majority of the 29 members remain functionally uncharacterized. Furthermore, the biological significance of the DNA and peptide sequence diversity, observed in the conserved motifs and domains found in the different AHL types, is a subject area that remains largely unexplored.
Transgenic plants overexpressing AtAHL20 flowered later than the wild type under both short and long days. Transcript accumulation analyses showed that 35S:AtAHL20 plants contained reduced FT, TSF, AGL8 and SPL3 mRNA levels. Similarly, overexpression of AtAHL20's orthologue in Camelina sativa, Arabidopsis' closely related Brassicaceae family member species, conferred a late-flowering phenotype via suppression of CsFT expression. However, overexpression of an aberrant AtAHL20 gene harboring a missense mutation in the AT-hook domain's highly conserved R-G-R core motif abolished the late-flowering phenotype. Data from targeted yeast-two-hybrid assays showed that AtAHL20 interacted with itself and several other Clade-A Type-I AHLs which have been previously implicated in flowering-time regulation: AtAHL19, AtAHL22 and AtAHL29.
We showed via gain-of-function analysis that AtAHL20 is a negative regulator of FT expression, as well as other downstream flowering time regulating genes. A similar outcome in Camelina sativa transgenic plants overexpressing CsAHL20 suggest that this is a conserved function. Our results demonstrate that AtAHL20 acts as a photoperiod-independent negative regulator of transition to flowering.
根据核苷酸和蛋白质序列进化差异，拟南芥 AHL 基因家族的 29 个成员分为三大类。这些差异包括内含子的存在与否、保守的 AT 钩和 PPC 结构域的类型和/或数量。AHL 基因家族成员分为两个系统发育枝，枝 A 和枝 B。大多数 29 个成员的功能仍未被阐明。此外，在不同 AHL 类型中发现的保守基序和结构域中观察到的 DNA 和肽序列多样性的生物学意义，在很大程度上仍是一个尚未探索的领域。
在短日和长日条件下，过表达 AtAHL20 的转基因植物比野生型开花晚。转录物积累分析表明，35S:AtAHL20 植物的 FT、TSF、AGL8 和 SPL3 mRNA 水平降低。同样，拟南芥近缘十字花科植物金鱼草中 AtAHL20 同源物的过表达通过抑制 CsFT 的表达导致晚花表型。然而，过表达含有 AT 钩结构域高度保守的 R-G-R 核心基序错义突变的异常 AtAHL20 基因则消除了晚花表型。靶向酵母双杂交试验的数据表明，AtAHL20 与自身以及其他几个已被证实参与开花时间调控的枝 A 型 I AHL 相互作用：AtAHL19、AtAHL22 和 AtAHL29。
通过功能获得分析，我们表明 AtAHL20 是 FT 表达以及其他下游开花时间调控基因的负调控因子。在过表达 CsAHL20 的金鱼草转基因植物中也得到了类似的结果，这表明这是一种保守的功能。我们的结果表明，AtAHL20 作为光周期独立的开花向期转换的负调控因子发挥作用。
