Abstract
BackgroundThe outer cell wall of the pollen grain (exine) is an extremely resistant structure containing sporopollenin, a mixed polymer made up of fatty acids and phenolic compounds. The synthesis of sporopollenin in the tapetal cells and its proper deposition on the pollen surface are essential for the development of viable pollen. The beginning of microsporogenesis and pollen maturation in perennial plants from temperate climates, such as peach, is conditioned by the duration of flower bud dormancy. In order to identify putative genes involved in these processes, we analyzed the results of previous genomic experiments studying the dormancy-dependent gene expression in different peach cultivars.ResultsThe expression of 50 genes induced in flower buds after the endodormancy period (flower-bud late genes) was compared in ten cultivars of peach with different dormancy behaviour. We found two co-expression clusters enriched in putative orthologs of sporopollenin synthesis and deposition factors in Arabidopsis. Flower-bud late genes were transiently expressed in anthers coincidently with microsporogenesis and pollen maturation processes. We postulated the participation of some flower-bud late genes in the sporopollenin synthesis pathway and the transcriptional regulation of late anther development in peach.ConclusionsPeach and the model plant Arabidopsis thaliana show multiple elements in common within the essential sporopollenin synthesis pathway and gene expression regulatory mechanisms affecting anther development. The transcriptomic analysis of dormancy-released flower buds proved to be an efficient procedure for the identification of anther and pollen development genes in perennial plants showing seasonal dormancy.
Highlights
The outer cell wall of the pollen grain is an extremely resistant structure containing sporopollenin, a mixed polymer made up of fatty acids and phenolic compounds
Several biochemical steps of sporopollenin biosynthesis and transcriptional regulatory circuits controlling pollen development have been elucidated in Arabidopsis by the analysis of male-sterile and exinedefective mutants [6]
Sporopollenin is successively secreted to the apoplast by specific transporters [12] and translocated to the microspores bound to proteins such as lipid transfer proteins (LTPs) and glycine rich proteins (GRPs) [6]
Summary
The outer cell wall of the pollen grain (exine) is an extremely resistant structure containing sporopollenin, a mixed polymer made up of fatty acids and phenolic compounds. Tapetal cells greatly contribute to pollen viability and function through the Recently, several biochemical steps of sporopollenin biosynthesis and transcriptional regulatory circuits controlling pollen development have been elucidated in Arabidopsis by the analysis of male-sterile and exinedefective mutants [6]. CoA-esterified fatty acids are alternatively reduced to form fatty alcohol derivatives or condensed with malonyl-CoA by LESS ADHESIVE POLLEN5/POLYKETIDE SYNTHASE B (LAP5/PKSB) and LAP6/PKSA, leading to alkyl pyrones [9,10]. These latter compounds are hydroxylated by TETRAKETIDE α-PYRONE REDUCTASE1 (TKPR1) and TKPR2 [11], and combined with phenylpropanoids to produce the sporopollenin precursors. A network of transcription factors containing basic helix-loop-helix (bHLH), plant homeodomain (PHD) finger, and MYB domains among others are likely regulating the expression of genes involved in these processes in the tapetum [13,14,15,16,17,18]
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