Transcriptomes of the anther sporophyte: availability and uses

Abstract

An anther includes sporophytic tissues of three outer cell layers and an innermost layer, the tapetum, which encloses a locule where the gametophytic microspores mature to become pollen. The sporophytic tissues also comprise some vascular cells and specialized cells of the stomium aligning the long anther axis for anther dehiscence. Studies of the anther sporophytic cells, especially the tapetum, have recently expanded from the use of microscopy to molecular biology and transcriptomes. The available sequencing technologies, plus the use of laser microdissection and in silico subtraction, have produced high-quality anther sporophyte transcriptomes of rice, Arabidopsis and maize. These transcriptomes have been used for research discoveries and have potential for future discoveries in diverse areas, including developmental gene activity networking and changes in enzyme and metabolic domains, prediction of protein functions by quantity, secretion, antisense transcript regulation, small RNAs and promoters for generating male sterility. We anticipate that these studies with rice and other transcriptomes will expand to encompass other plants, whose genomes will be sequenced soon, with ever-advancing sequencing technologies. In comprehensive gene activity profiling of the anther sporophyte, studies involving transcriptomes will spearhead investigation of the downstream gene activity with proteomics and metabolomics.

Fig. 1

Production and studies of anther sporophyte transcriptomes. Whole anthers (or flowers of Arabidopsis) or tapetum cells and microspores dissected via laser capture microdissection (LCM) from wild-type or mutant plants are used for transcriptome construction with microarray, massive parallel signature sequencing (MPSS), sequencing-by-synthesis (SBS) or RNA-Seq technologies. The transcriptomes are further analyzed directly or via in silico subtraction to identify sporophyte-specific genes and potential gene functions.

Fig. 2

A proposed gene regulation network of anther development in Arabidopsis. The diagram shows the transcription factors controlling tapetum cell formation, differentiation and programmed cell death. The tapetum cells in turn control the maturation of microspores. This figure is adopted from Wilson and Zhang (2009) and Murmu et al. (2010), which describe the names and potential actions of the transcription factors.

Fig. 3

A model of exine precursor biosynthesis in the tapetum cells and transport of the precursors from the tapetum cell to the microspore surface. Fatty acids are synthesized in the plastid and transferred to the endoplasmic reticulum or cytosol for modifications. The resulting fatty components are covalently linked with phenylpropanoids to form exine precursors. The precursors are transported from the tapetum cell to the microspore surface via an ABC transporter or vesiculation, with the aid of lipid transfer proteins (LTPs). The model was drawn from results of Huang et al. (2009), Grienenberger et al. (2010) and Ariizumi and Toriyame (2011), which include the complete names of the abbreviated protein names.