The mac1 Gene: Controlling the Commitment to the Meiotic Pathway in Maize

Abstract

The switch from the vegetative to the reproductive pathway of development in flowering plants requires the commitment of the subepidermal cells of the ovules and anthers to enter the meiotic pathway. These cells, the hypodermal cells, either directly or indirectly form the archesporial cells that, in turn, differentiate into the megasporocytes and microsporocytes. We have isolated a recessive pleiotropic mutation that we have termed multiple archesporial cells1 (macl) and located it to the short arm of chromosome 10. Its cytological phenotype suggests that this locus plays an important role in the switch of the hypodermal cells from the vegetative to the meiotic (sporogenous) pathway in maize ovules. During normal ovule development in maize, only a single hypodermal cell develops into an archesporial cell and this differentiates into the single megasporocyte. In macl mutant ovules several hypodermal cells develop into archesporial cells, and the resulting megasporocytes undergo a normal meiosis. More than one megaspore survives in the tetrad and more than one embryo sac is formed in each ovule. Ears on mutant plants show partial sterility resulting from abnormalities in megaspore differentiation and embryo sac formation. The sporophytic expression of this gene is therefore also important for normal female gametophyte development.

The Maize Megagametophyte

“…The archesporial cell directly differentiates into the megasporocyte, or megaspore mother cell (MMC), and elongates perpendicular to the ovule surface along the m-c axis before meiosis (Figure 1a). In the maize multiple archesporial cells1 (mac1) mutant several adjacent cells develop as archesporial cells, suggesting that archesporial cell fate is actively suppressed in cells adjacent to the archesporium (Sheridan et al 1996). Polar distribution of cytoplasmic components along the long m-c axis of the megasporocyte is present in the MMC before meiosis.…”

Organ geometry channels reproductive cell fate in the Arabidopsis ovule primordium

“…Although SMC singleness may appear to be robust, more than one SMC candidate per primordium is occasionally seen, yet at different frequencies depending on the specific Arabidopsis accession (~5% in Landsberg erecta [L er ], 10% in Columbia [Col-0], 27% in Monterrosso [Mr-0]), ( Grossniklaus and Schneitz, 1998 ; Rodríguez-Leal et al, 2015 ). Arabidopsis , maize, and rice mutants in which SMC singleness is compromised have unveiled the role of regulatory pathways involving intercellular signaling, small RNAs, as well as DNA and histone methylation ( Garcia-Aguilar et al, 2010 ; Mendes et al, 2020 ; Nonomura et al, 2003 ; Olmedo-Monfil et al, 2010 ; Schmidt et al, 2011 ; Sheridan et al, 1996 ; Sheridan et al, 1999 ; Su et al, 2020 ; Su et al, 2017 ; Zhao et al, 2008 ). As the SMC forms, cell-cycle regulation contributes to the stabilization of its fate in a cell-autonomous manner through cyclin-dependent kinase (CDK) inhibitors and RETINOBLASTOMA-RELATED1 (RBR1) ( Cao et al, 2018 ; Zhao et al, 2017 ).…”

Rice MutLγ, the MLH1–MLH3 heterodimer, participates in the formation of type I crossovers and regulation of embryo sac fertility

“…Then, though three consecutive nuclear mitosis, the FM further develops into the seven‐celled embryo sac (Drews and Koltunow, 2011; Nakajima, 2018). The main studies focusing on Arabidopsis , for example, show that SPL , WUS , MAC1 are involved in regulating the transformation of somatic cells to germ cells, MSP1 in regulation of the number of MMC, and SWI1 , ARP6 in regulation of meiosis of MMC (Boateng et al, 2008; Lieber et al, 2011; Nonomura et al, 2003; Qin et al, 2014; Sheridan et al, 1996; Yang et al, 1999). At FG genesis, RBR , LACHESIS , BLH1 , MYB64 and MYB119 are involved in the regulation of mitosis of FM and the cellularization of FG (Gross‐Hardt et al, 2007; Ingouff et al, 2009; Pagnussat et al, 2007; Rabiger and Drews, 2013).…”