A framework for evaluating developmental defects at the cellular level: An example from ten maize anther mutants using morphological and molecular data

Abstract

In seed plants, anthers are critical for sexual reproduction, because they foster both meiosis and subsequent pollen development of male germinal cells. Male-sterile mutants are analyzed to define steps in anther development. Historically the major topics in these studies are meiotic arrest and post-meiotic gametophyte failure, while relatively few studies focus on pre-meiotic defects of anther somatic cells. Utilizing morphometric analysis we demonstrate that pre-meiotic mutants can be impaired in anticlinal or periclinal cell division patterns and that final cell number in the pre-meiotic anther lobe is independent of cell number changes of individual differentiated somatic cell types. Data derived from microarrays and from cell wall NMR analyses allow us to further refine our understanding of the onset of phenotypes. Collectively the data highlight that even minor deviations from the correct spatiotemporal pattern of somatic cell proliferation can result in male sterility in Zea mays.

MS23, a master basic helix-loop-helix factor, regulates the specification and development of tapetum in maize

“…A relatively large size, the 30-day-long period of anther development, and the regularity of ontogeny in which anther length allows accurate developmental staging have facilitated dissection and confocal reconstruction of cell division and expansion patterns in maize anthers (Kelliher and Walbot, 2011). Additionally, there are hundreds of male-sterile mutants (Skibbe and Schnable, 2005) including a subset disrupting somatic lobe development prior to meiosis Egger and Walbot, 2016). These maize resources were developed in part to facilitate hybrid seed production using male-sterile plants as ear parents with pollen supplied by a male-fertile partner line.…”

GROWTH-REGULATING FACTOR and GRF-INTERACTING FACTOR Specify Meristematic Cells of Gynoecia and Anthers

“…As for the anther, a host of genes have been known to be involved in its development (Ma, 2005;Egger and Walbot, 2016). Among them, only a few genes function in specifying archesporial cell fate and/or delineating archesporial and somatic cells.…”

“…Each lobe internally develops a microsporangium that consists of three outer concentric parietal layers (i.e. endothecium, middle layer, and tapetum), and the microsporangium harbors pollen mother cells (PMCs; Sanders et al, 1999;Egger and Walbot, 2016;Supplemental Fig. S1).…”

A renaissance in plant development

“…Nonetheless, highly regulated cell divisions underlie plant morphogenesis and organogenesis. Egger and Walbot (Egger and Walbot, 2016) provide "a framework for evaluating developmental defects at the cellular level". In this sweeping survey of 24 pre-meiotic male sterile mutants in maize, confocal microscopy is used to analyze the role of cell proliferation defects and cell morphology in producing defined cell layers of the maize anther lobes.…”