MYB64 and MYB119 Are Required for Cellularization and Differentiation during Female Gametogenesis in Arabidopsis thaliana

Abstract

In angiosperms, the egg cell forms within the multicellular, haploid female gametophyte. Female gametophyte and egg cell development occurs through a unique process in which a haploid spore initially undergoes several rounds of synchronous nuclear divisions without cytokinesis, resulting in a single cell containing multiple nuclei. The developing gametophyte then forms cell walls (cellularization) and the resulting cells differentiate to generate the egg cell and several accessory cells. The switch between free nuclear divisions and cellularization-differentiation occurs during developmental stage FG5 in Arabidopsis, and we refer to it as the FG5 transition. The molecular regulators that initiate the FG5 transition during female gametophyte development are unknown. In this study, we show using mutant analysis that two closely related MYB transcription factors, MYB64 and MYB119, act redundantly to promote this transition. MYB64 and MYB119 are expressed during the FG5 transition, and most myb64 myb119 double mutant gametophytes fail to initiate the FG5 transition, resulting in uncellularized gametophytes with supernumerary nuclei. Analysis of cell-specific markers in myb64 myb119 gametophytes that do cellularize suggests that gametophytic polarity and differentiation are also affected. We also show using multiple-mutant analysis that MYB119 expression is regulated by the histidine kinase CKI1, the primary activator of two-component signaling (TCS) during female gametophyte development. Our data establish a molecular pathway regulating the FG5 transition and implicates CKI1-dependent TCS in the promotion of cellularization, differentiation, and gamete specification during female gametogenesis.

Isolation and characterization of a copalyl diphosphate synthase gene promoter from Salvia miltiorrhiza

“…3) [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60]. Comparison of the obtained data with trans-factors identified by the in silico searches of S. miltiorrhiza CPS promoter showed no common protein (Tab.…”

“…The results of in silico searches and microarray co-expression studies differ with regard to plant morphogenesis. While the in silico studies suggest that CPS promoter has a potential role in plant embryogenesis and leaf development, the microarray co-expression tests indicate that the CPS promoter has potential participation in a broader range of morphogenesis processes as pollen, sieve, seed, ovule, and gametophyte development [25,28,[44][45][46][47][48][49][50][51].…”

“…The microarray data implied a role of A. thaliana CPS in development of such elements as pollen, sieve, seed, ovule, and gametophyte (Tab. 3) [44,[46][47][48][49][50][51]. According to the in silico searches, the S. miltiorrhiza CPS promoter should participate rather in leaf development (Tab.…”

Plant germline formation: common concepts and developmental flexibility in sexual and asexual reproduction

“…Although related to the Arabidopsis histidine kinases (AHKs) AHK2, AHK3 and AHK4, which act as cytokinin receptors, CKI1 lacks a cytokinin-binding domain and activates the cytokinin signalling pathway in the absence of cytokinin (Kakimoto, 1996;Nakamura et al, 1999;Urao et al, 2000;Hwang and Sheen, 2001;Yamada et al, 2001;Mähönen et al, 2006). Arabidopsis double mutants affecting MYB-DOMAIN PROTEIN64 (MYB64) and MYB119, which encode two closely related R2R3-MYB domain transcription factors, also display a cki1-like phenotype (Table 3; Rabiger and Drews, 2013). Double mutant myb64 myb119 gametophytes undergo extra mitotic division cycles and usually fail to cellularize (Rabiger and Drews, 2013).…”

An EAR-Dependent Regulatory Module Promotes Male Germ Cell Division and Sperm Fertility in Arabidopsis

“…The cellularization and differentiation of cells in the embryo sac appear to be transcriptionally regulated (Rabiger and Drews, 2013), and mechanisms involving RNA splicing and auxin and peptide signaling specify female gametic cells (Gross-Hardt et al, 2007;Pagnussat et al, 2009;Lieber et al, 2011;Lituiev et al, 2013). For male germline development, a regulatory framework for cell cycle progression and gamete specification has been established Borg and Twell, 2010;Twell, 2011).…”