Anther and pollen development: A conserved developmental pathway

Abstract

Pollen development is a critical step in plant development that is needed for successful breeding and seed formation. Manipulation of male fertility has proved a useful trait for hybrid breeding and increased crop yield. However, although there is a good understanding developing of the molecular mechanisms of anther and pollen anther development in model species, such as Arabidopsis and rice, little is known about the equivalent processes in important crops. Nevertheless the onset of increased genomic information and genetic tools is facilitating translation of information from the models to crops, such as barley and wheat; this will enable increased understanding and manipulation of these pathways for agricultural improvement.

Keywords: Anther; Arabdiopsis; cereals; comparative biology; pollen.

Figure 1

Anther and pollen development sections of (A–E) Arabidopsis and (F–J) barley Anther and pollen development follows a similar pathway in Arabidopsis and barley (A and F): Secondary sporogenous cells to pollen mother cells. Four cell layers surrounding the anther. (B and G): Microspore release from the tetrad; the tapetum becomes vacuolated. (C and H): Free microspores; middle layer becomes crushed and the prominent tapetum starts to degenerate. (D and I): Microspores become vacuolated and tapetum degenerates. (E and J): Trinuclear pollen; septum breakage and pollen release. Ep, epidermis; En, endothecium; Mc, microspores; Ml, middle layer; Tp, tapetum; Tt, tetrad. Bars = 50 μm.

Figure 2

Anther and pollen development gene regulation network for Arabidopsis and rice from anther cell specification to mature pollen formation Comparisons between species show similarities in the regulation of pollen development; unconnected regions and “?” indicate where regulatory network is still undefined. Colors correspond to equivalent orthologs.

Figure 3

Transverse sections through barley anthers of sterile HvMS1‐RNAi silencing lines and wild type (WT) (A, B) Section of a wild type anther at late free microspore stage. Middle layer has disappeared but the tapetum is still intact. (C, D) HvMS1‐RNAi lines at free microspore stage. Silencing lines showed early tapetum degeneration when compared to the wild type (B). Ep, epidermis; En, endothecium; Tp, tapetum. Bar: A and C: 50 μm, B and D: 20 μm.

Figure 4

Diagram showing the various steps to identify putative orthologous genes in barley and wheat starting from an Arabidopsis gene Several bioinformatics tools are available to compare/find sequences, analyze expression patterns, establish phylogenetic trees or synteny analysis. URL; Gramene: http://www.gramene.org/; NCBI: http://blast.ncbi.nlm.nih.gov/Blast.cgi; RicexPro: http://ricexpro.dna.affrc.go.jp/; URGI: http://wheat-urgi.versailles.inra.fr/Seq-Repository/BLAST; Barley IPK database: http://webblast.ipk-gatersleben.de/barley/.