Mira Mohammed M, Hill Robert D, Stasolla Claudio
Department of Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.
Department of Botany, Faculty of Science, Tanta University, Tanta, 31527, Egypt.
Planta. 2025 Jan 22;261(2):42. doi: 10.1007/s00425-025-04617-0.
Phytoglobin1 promotes Arabidopsis somatic embryogenesis through the mediation of ethylene and the ERFVII HRE2. Generation of somatic embryos in Arabidopsis (Arabidopsis thaliana) is a two-step process, encompassing an induction phase where embryogenic tissue (ET) is formed followed by a developmental phase encouraging the growth of the embryos. Using previously characterized transgenic lines dysregulating the class 1 Phytoglobin (Pgb1) we show that suppression of Pgb1 decreases somatic embryogenesis (SE). Both the formation of ET (SE efficiency) and production of SE (SE productivity) are repressed in explants where Pgb1 is downregulated. The levels of Pgb1 transcripts peak in the middle phase of the induction period coinciding with the formation of the ET. Presence of Pgb1 results in a transcriptional depression of ethylene synthesis and of the class VII ethylene transcription factor (ERFVII) HRE2. Suppression of ethylene after day 3 of induction, or repression of HRE2 are needed for SE efficiency and the decline in HRE2 transcripts appears to be independent from the level of ethylene. Over-expression of HRE2 inhibits SE efficiency regardless of the expression of Pgb1. Furthermore, a functional HRE2 generates a peak in Pgb1 transcripts during the middle induction phase. The expression of another ERFVII, RAP2.12, is not altered by changes in Pgb1 levels, and disruption of RAP2.12 has no effect on SE efficiency although it enhances SE productivity in a Pgb1-independent fashion. Thus, Pgb1 is an important regulator of Arabidopsis SE, and its action is linked to changes in ethylene and the ERFVII HRE2.
植物血红蛋白1通过乙烯和ERFVII家族的HRE2介导促进拟南芥体细胞胚胎发生。拟南芥（Arabidopsis thaliana）体细胞胚胎的产生是一个两步过程，包括胚胎发生组织（ET）形成的诱导阶段，随后是促进胚胎生长的发育阶段。利用先前鉴定的失调1类植物血红蛋白（Pgb1）的转基因株系，我们发现Pgb1的抑制会降低体细胞胚胎发生（SE）。在Pgb1下调的外植体中，ET的形成（SE效率）和SE的产生（SE生产力）均受到抑制。Pgb1转录本水平在诱导期的中期达到峰值，与ET的形成一致。Pgb1的存在导致乙烯合成和VII类乙烯转录因子（ERFVII）HRE2的转录抑制。诱导第3天后乙烯的抑制或HRE2的抑制是SE效率所必需的，并且HRE2转录本的下降似乎与乙烯水平无关。无论Pgb1的表达如何，HRE2的过表达均抑制SE效率。此外，功能性HRE2在诱导中期使Pgb1转录本出现峰值。另一个ERFVII家族成员RAP2.12的表达不会因Pgb1水平的变化而改变，并且RAP2.12的破坏对SE效率没有影响，尽管它以不依赖Pgb1的方式提高了SE生产力。因此，Pgb1是拟南芥SE的重要调节因子，其作用与乙烯和ERFVII家族的HRE2的变化有关。
