Cytological Characterization and Allelism Testing of Anther Developmental Mutants Identified in a Screen of Maize Male Sterile Lines

Abstract

Proper regulation of anther differentiation is crucial for producing functional pollen, and defects in or absence of any anther cell type result in male sterility. To deepen understanding of processes required to establish premeiotic cell fate and differentiation of somatic support cell layers a cytological screen of maize male-sterile mutants has been conducted which yielded 42 new mutants including 22 mutants with premeiotic cytological defects (increasing this class fivefold), 7 mutants with postmeiotic defects, and 13 mutants with irregular meiosis. Allelism tests with known and new mutants confirmed new alleles of four premeiotic developmental mutants, including two novel alleles of msca1 and single new alleles of ms32, ms8, and ocl4, and two alleles of the postmeiotic ms45. An allelic pair of newly described mutants was found. Premeiotic mutants are now classified into four categories: anther identity defects, abnormal anther structure, locular wall defects and premature degradation of cell layers, and/or microsporocyte collapse. The range of mutant phenotypic classes is discussed in comparison with developmental genetic investigation of anther development in rice and Arabidopsis to highlight similarities and differences between grasses and eudicots and within the grasses.

Spatiotemporally dynamic, cell-type–dependent premeiotic and meiotic phasiRNAs in maize anthers

“…To gain insight into cell type contributions to phasiRNA production, RNAs were analyzed from developmental mutants defective in specific anther cell types ( Fig. 3A and Dataset S3) (20). OCL4 (OUTER CELL LAYER 4) is an epidermal-specific transcription factor repressing periclinal divisions in the adjacent subepidermal endothecial cells (21), presumably through a mobile signal (22).…”

Construction of a multicontrol sterility system for a maize male‐sterile line and hybrid seed production based on the ZmMs7 gene encoding a PHD‐finger transcription factor

“…Nuclear‐encoded male sterility (NMS) or GMS results from mutations in the nuclear genome, which is a common spontaneous phenomenon in flowering plants (Kaul, ). To date, hundreds of genetic male‐sterile mutants have been identified and described in maize (Timofejeva et al ., ). Most of these mutants are controlled by a recessive gene, which provides an excellent genetic means of emasculation for hybrid seed production in maize.…”

“…Based on the critical time points of male sterility conversion, the male‐sterile mutants can be classified as premeiotic, meiotic and postmeiotic. In previous reports, hundreds of maize male‐sterile mutants were identified and classified into the above three classes based on cytological characterization and allelism testing (Timofejeva et al ., ). Twenty‐two maize male‐sterile mutants with premeiotic developmental defects were used to evaluate the detailed cytological characteristics.…”

Unresolved issues in pre-meiotic anther development

“…Historically most studies have focused on meiosis and pollen biogenesis, with the assumption that a simple lineage model explained how the typical four somatic wall layers with central archesporial (AR) cells arose from a stamen primordium (Figure 1A). Starting with recovery and analysis of mutants defective in cell fate specification about 20 years ago (Sheridan et al, 1996; Canales et al, 2002; Zhao et al, 2002; reviewed by Ma, 2005), new theories and molecular insights into the first phase of anther development were proposed, disputed, and continue to be revised and elaborated.…”