Anther development in flowering plants involves the formation of several cell types, including the tapetal and pollen mother cells. The use of genetic and molecular tools has led to the identification and characterization of genes that are critical for normal cell division and differentiation in Arabidopsis early anther development. We review here several recent studies on these genes, including the demonstration that the putative receptor protein kinases BAM1 and BAM2 together play essential roles in the control of early cell division and differentiation. In addition, we discuss the hypothesis that BAM1/2 may form a positive-negative feedback regulatory loop with a previously identified key regulator, SPOROCYTELESS (also called NOZZLE), to control the balance between sporogenous and somatic cell types in the anther. Furthermore, we summarize the isolation and functional analysis of the DYSFUNCTIONAL TAPETUM1 (DYT1) gene in promoting proper tapetal cell differentiation. Our finding that DYT1 encodes a putative transcription factor of the bHLH family, as well as relevant expression analyses, strongly supports a model that DYT1 serves as a critical link between upstream factors and downstream target genes that are critical for normal tapetum development and function. These studies, together with other recently published works, indicate that cell-cell communication and transcriptional control are key processes essential for cell fate specification in anther development.Key words: anther development; Arabidopsis; signaling; tapetum; transcription factor. Available online at www.blackwell-synergy.com/links/toc/jipb, www.jipb.netIn flowering plants, reproduction depends on the production of pollen grains in the male reproductive organ called the anther.To produce pollen, several cell types must be formed during early anther development (Goldberg et al. 1993;Ma 2005). The progenitor of pollen is called the pollen mother cell, which undergoes meiosis to produce four microspores that develop into four pollen grains. At the time when the pollen mother cells are formed, the anther has four similarly shaped lobes, each of which has five cell types. On the surface is the epidermis, a cell layer that is derived from the L1 layer of the anther primordium. Interior of the epidermis is the endothecium, which surrounds the middle layer. Interior of the middle layer is the tapetum, which encircles the pollen mother cells and is known to be critical for pollen development from the microspore (Mariani et al. 1990;Goldberg et al. 1993;Ma 2005 Hord et al. (2006) showed that the BAM1 and BAM2 putative receptor-like protein kinases are critical for very early development of the Arabidopsis anther. BAM1 and BAM2 are closely related in sequence to the CLAVATA1 (CLV1) putative receptor-like protein kinase, which has been shown to be critical for the homeostasis of the stem cell pool in the shoot apical meristem (Clark et al. 1997). CLV1, BAM1, BAM2, and a fourth gene called BAM3, form a small clade with strong support Hord et al. 2...
SummaryCanola (Brassica napus) is a widely cultivated species and provides important resources of edible vegetable oil, biodiesel production and animal feed. Seed development in Arabidopsis and canola shares a similar path: an early proliferation of endosperm to form a large seed cavity, followed by a second phase in which the embryo grows to replace the endosperm. In Arabidopsis, the seed reaches almost its final volume before the enlargement of the embryo. SHORT HYPOCOTYL UNDER BLUE1 (SHB1) is a key regulatory gene of seed development with a broad expression beyond endosperm development. By contrast, its two target genes, MINISEED3 (MINI3) and HAIKU2 (IKU2), are narrowly expressed in early developing endosperm and early embryo.We overexpressed SHB1 in canola to explore the possibility of altering seed development. As an alternative strategy, we expressed the canola IKU2 ortholog in Arabidopsis endosperm under the control of a stronger MINI3 promoter.SHB1 targeted canola orthologs of Arabidopsis MINI3 and IKU2 and caused a significantly increased seed mass. Overaccumulation of IKU2 in the early stage of Arabidopsis seed development also significantly increased the final seed mass.Our studies provide a strong case for increasing the final seed mass by manipulating endosperm proliferation at a rather early developmental stage in crops.
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