By Mingsong Zhu and Xiaoping Gou
Mingsong Zhu, Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University
Xiaoping Gou, Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University
Background: The sexual reproduction process of angiosperms requires correct development of the female gametophyte, or In Arabidopsis, CYTOKININ INDEPENDENT 1 (CKI1), a histidine kinase that can constitutively activate the cytokinin signaling pathway, plays an essential role in central cell specification, which is also dependent on ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN 2/3/5 (AHP2/3/5).
Question: Although type-B ARABIDOPSIS RESPONSE REGULATORS (ARRs) usually function downstream of the cytokinin signaling pathway as core transcription factors to regulate various biological processes during plant growth, it is not known which ARRs play key roles downstream of the CKI1–AHP2/3/5 module to specify the central cell.
Findings: We identified three type-B ARRs, ARR10, ARR12, and ARR18, which were polarly localized at the chalazal pole of the embryo sac after stage FG4. Genetic analyses revealed that the arr10 12 18 female gamete was never transmitted to the progeny. Expression pattern analyses of embryo sac cell markers revealed that the central cell identity was lost and the egg cell and synergid cell identities extended to the chalazal end in the arr10 12 18 embryo sacs. Genetic analysis showed that CKI1, AHP2/3/5, and ARR10/12/18 function in a common pathway to specify the central cell, which was also supported by transcriptomic results. In addition, constitutively activated ARR10/12/18 partially rescued the central cell defects of cki1 and ahp2/3/5. We demonstrated that the CKI1–AHP2/3/5–ARR10/12/18 signaling module has crucial functions in determining cell fates of the female gametophyte.
Next steps: We do not know the direct downstream components of the CKI1–AHP2/3/5–ARR10/12/18 signaling module during female gametophyte development. Moreover, the mechanism controlling polar localization of CKI1 and ARR10/12/18 in the chalazal pole of the embryo sac is worthy of further investigation.
Mingsong Zhu, Liang Tao, Jinghua Zhang, Ruini Liu, Hongai Tian, Chong Hu, Yafen Zhu, Meizhen Li, Zhuoyun Wei, Jing Yi, Jia Li, Xiaoping Gou. (2022). The type-B response regulators ARR10, ARR12 and ARR18 specify the central cell in Arabidopsis. Plant Cell. https://doi.org/10.1093/plcell/koac285