Department of Plant Biology, Ecology, and Evolution, Oklahoma State University, 301 Physical Sciences, Stillwater, OK 74078, U.S.A.
Biosci Rep. 2022 Sep 30;42(9). doi: 10.1042/BSR20221504.
The plant hormone auxin suppresses seed germination, but how auxin does it remains poorly understood. While studying the functions of the AUXIN SIGNALING F-BOX (AFB) auxin co-receptors in Arabidopsis, we consistently isolated AFB1 and AFB5 in reproductive tissues in co-immunoprecipitation experiments using their interacting protein ASK1 as the bait. However, T2 seeds of the AFB1 or AFB5 transgenic lines generated for the co-immunoprecipitation experiments frequently failed to germinate, which led to the studies of seed germination in these plants and afb1 and afb5 mutants, and AFB1 and AFB5 expression in nearly mature fruit and imbibed seeds using AFB1:GUS and AFB5:GUS lines. We found that AFB1 and AFB5 acted in maternal tissues to suppress seed germination and their effects were positively correlated with the plants' sensitivity to indole acetic acid. Conversely, afb1 and afb5 single mutants exhibited faster seed germination than the wild type and the seeds of the afb1-5afb5-5 double mutant germinated even faster than those of the afb1-5 and afb5-5 single mutants. Seed germination of the afb1-5afb5-5 double mutant also exhibited higher sensitivity to gibberellic acid than that of the wild-type and the afb1-3, afb1-5 and afb5-5 single mutants. Both AFB1 and AFB5 were expressed in the funiculus during seed maturation, and AFB1 was also transiently expressed in a small chalazal region surrounding the hilum in the seed coat during seed imbibition. Therefore, AFB1 and AFB5 likely suppress seed germination in the funiculus and AFB1 also briefly suppresses seed germination in the chalaza during seed imbibition.
植物激素生长素抑制种子萌发，但生长素如何做到这一点仍知之甚少。在研究拟南芥 AUXIN SIGNALING F-BOX (AFB) 生长素共受体的功能时，我们使用其相互作用蛋白 ASK1 作为诱饵，在共免疫沉淀实验中一致分离到生殖组织中的 AFB1 和 AFB5。然而，用于共免疫沉淀实验的 AFB1 或 AFB5 转基因系的 T2 种子经常无法萌发，这导致我们对这些植物以及 afb1 和 afb5 突变体的种子萌发以及近成熟果实和吸胀种子中的 AFB1 和 AFB5 表达进行了研究，使用 AFB1:GUS 和 AFB5:GUS 系。我们发现 AFB1 和 AFB5 在母体组织中发挥作用，抑制种子萌发，它们的作用与植物对吲哚乙酸的敏感性呈正相关。相反，afb1 和 afb5 单突变体的种子萌发速度比野生型快，afb1-5afb5-5 双突变体的种子萌发速度甚至比 afb1-5 和 afb5-5 单突变体的种子更快。afb1-5afb5-5 双突变体的种子萌发对赤霉素的敏感性也高于野生型和 afb1-3、afb1-5 和 afb5-5 单突变体。AFB1 和 AFB5 在种子成熟过程中均在珠柄中表达，并且在种子吸胀过程中 AFB1 也短暂在种皮的珠孔周围的一个小合点区域表达。因此，AFB1 和 AFB5 可能在珠柄中抑制种子萌发，并且 AFB1 在种子吸胀过程中也短暂抑制合点中的种子萌发。
