In Arabidopsis thaliana, the female gametophyte consists of two synergid cells, an egg cell, a diploid central cell, and three antipodal cells. CYTOKININ INDEPENDENT 1 (CKI1), a histidine kinase constitutively activating the cytokinin signaling pathway, specifies the central cell and restricts the egg cell. However, the mechanism regulating CKI1-dependent central cell specification is largely unknown. Here, we showed that the type-B ARABIDOPSIS RESPONSE REGULATORS10, 12, and 18 (ARR10/12/18) localize at the chalazal pole of the female gametophyte. Phenotypic analysis showed that the arr10 12 18 triple mutant is female sterile. We examined the expression patterns of embryo sac marker genes and found that the embryo sac of arr10 12 18 plants had lost central cell identity, a phenotype similar to that of the Arabidopsis cki1 mutant. Genetic analyses demonstrated that ARR10/12/18, CKI1, and ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN2, 3, and 5 (AHP2/3/5) function in a common pathway to regulate female gametophyte development. In addition, constitutively activated ARR10/12/18 in the cki1 embryo sac partially restored the fertility of cki1. Results of transcriptomic analysis supported the conclusion that ARR10/12/18 and CKI1 function together to regulate the identity of the central cell. Our results demonstrated that ARR10/12/18 function downstream of CKI1-AHP2/3/5 as core factors to determine cell fate of the female gametophyte.

中文翻译：

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B 型反应调节因子 ARR10、ARR12 和 ARR18 指定拟南芥中的中央细胞。

在拟南芥中，雌配子体由两个助细胞、一个卵细胞、一个二倍体中央细胞和三个反足细胞组成。细胞分裂素独立 1 (CKI1) 是一种组成型激活细胞分裂素信号通路的组氨酸激酶，可指定中央细胞并限制卵细胞。然而，调节 CKI1 依赖性中枢细胞规范的机制在很大程度上尚不清楚。在这里，我们发现 B 型拟南芥响应调节器 10、12 和 18 (ARR10/12/18) 位于雌配子体的合点极。表型分析表明arr10 12 18 三重突变体是雌性不育的。我们检查了胚囊标记基因的表达模式，发现 arr10 12 18 植物的胚囊已经失去了中心细胞身份，其表型与拟南芥 cki1 突变体相似。遗传分析表明，ARR10/12/18、CKI1 和拟南芥组氨酸磷酸转移蛋白 2、3 和 5 (AHP2/3/5) 在调节雌配子体发育的共同途径中发挥作用。此外，cki1胚囊中组成型激活的ARR10/12/18部分恢复了cki1的生育能力。转录组分析结果支持以下结论：ARR10/12/18 和 CKI1 共同发挥作用来调节中枢细胞的身份。我们的结果表明，ARR10/12/18 在 CKI1-AHP2/3/5 下游发挥作用，作为决定雌配子体细胞命运的核心因素。