Minisymposium 15: Pollen Biology

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Abs # M1501: The BAM1/BAM2 LRR-Receptor-Like Kinases are Essential for Normal Cell Fate Specification in the Early Arabidopsis Anther

Presenter:	Hord, Carey L. H.       Contact Presenter
Authors	Hord, Carey L. H. (A) (B)  Chen, Changbin  (A)   DeYoung, Brody J. (C)   Clark, Steven E. (C)   Ma, Hong  (A) (B)
Affiliations:	(A): Department of Biology and the Huck Institutes for the Life Sciences, The Pennsylvania State University (B): The Integrative Biosciences Graduate Degree Program, The Pennsylvania State University (C): Department of Molecular, Cellular, and Developmental Biology, University of Michigan

Cellular division and differentiation are the mechanisms by which multicellular organisms develop. In flowering plants, anther development involves the coordinated formation and differentiation of several adjacent cell types, which are required for normal male fertility. This includes the generation of the the endothecial, middle, and tapetal cell layers that form sequential rings around pollen mother cells (PMCs). The PMCs undergo meiosis to produce microspores, and the somatic cell layers, particularly the tapetum, play critical roles in supporting the development of microspores into mature pollen grains. Maximum success in male reproduction requires a balance between the number of the reproductive cells (PMCs) and those of the somatic cells. Currently, only a few genes are known to be involved in the development of these different cell layers. One of them, SPL/NZZ, is activated by AG and appears to function very early in anther development as the spl/nzz mutant does not form the normal anther cell layers. BAM1 and BAM2 encode CLAVATA1 (CLV1)-related leucine-rich repeat receptor protein kinases. BAM1 and BAM2 likely have redundant functions, as disruption of either does not appear to affect plant development. We have analyzed anther development in the bam1 bam2 flowers and found that bam1 bam2 anthers lack the endothecial, middle, and tapetal cell layers. Further characterization of the bam1 bam2 anthers revealed that the cells interior to the epidermis acquire characteristics of PMCs, indicating a change in cell fate at a very early stage of anther development. In addition, the pollen mother-like cells (PMLs) degenerate prior to the completion of meiosis, suggesting that these cells are defective. Analysis of BAM1 and BAM2 expression showed that they are expressed in both the archesporial cells and later in the PMCs. This supports both an early role in promoting the somatic cell fates and a subsequent function in the PMCs. In addition, our analysis revealed that BAM1 and/or BAM2 and SPL/NZZ may form a regulatory feedback loop that regulates the balance between the sporogenous and somatic cell fates during anther development. Therefore, analysis of BAM1 and BAM2 uncovered a cell-cell communication process important for early anther development, including aspects of cell division and differentiation. This may have implications for the evolution of multiple signaling pathways in specifying the cell types for microsporogenesis.