Transcriptomic analysis of heteromorphic stamens in Cassia biscapsularis L.

Zhonglai Luo,Dianxiang Zhang,Zhongtao Zhao,Jin Hu

doi:10.1038/srep31600

Zhonglai Luo, Dianxiang Zhang + Show 2 more

Open Access

https://doi.org/10.1038/srep31600

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Abstract

Hermaphroditic flowers have evolved primarily under the selection on male function. Evolutionary modification often leads to stamen differentiation within flowers, or “heteranthery”, a phenomenon intrigued scientists since the 18th century until recently. However, the genetic basis and molecular regulation mechanism has barely been touched. Here we conducted comparative transcriptome profiling in Cassia biscapsularis L., a heterantherous species with representative patterns of stamen differentiation. Numerous differentially expressed genes (DEGs) were detected between the staminodes (the degenerated stamens) and fertile stamens, while much fewer genes differentially expressed among the three sets of fertile stamens. GO term enrichment and KEGG pathway analysis characterized functional properties of DEGs in different stamen types. Transcripts showing close correlation between expression pattern and stamen types were identified. Transcription factors from the bHLH family were suggested to have taken crucial part in the formation of staminodes. This first global transcriptomic analysis focusing on stamen differentiation opens the door toward a more comprehensive understanding on the molecular regulation of floral organ evolution. Especially, the generated unigene resource would be valuable for developing male sterile lines in agronomy.

Highlights

Flower form evolution played key role in angiosperm radiation[1,2]
The modification of androecia sometimes results in sterile stamens, or staminodes, which have lost the function of producing fertile pollen[6]
We firstly focused on the transcriptomic changes between fertile stamens (L, M, S) and the staminodes (St), which exhibited the greatest difference

Summary

Introduction

Flower form evolution played key role in angiosperm radiation[1,2]. The “enigmatic” diversity of angiosperm floral organs has intrigued both the botanists and evolutionary biologists ever since the 18th century[3]. During the evolution of floral forms, androecia (the set of a flower’s stamens) modification frequently resulted in stamen repression, stamen loss or transformation of stamen function[6]. This leads to intrafloral stamen differentiation (differentiation of stamens within flowers), and the formation of heteromorphic stamens, or “heteranthery”, a within-flower polymorphism documented in many unrelated families[7,8]. Heteranthery, the presence of stamens in a flower that differ notably in size, colors and/or shape, and presumably with different functions, was first described more than one hundred years ago[9] Darwin hypothesized that it reflects a “division of labor” among stamens[9]. The molecular mechanisms behind intrafloral stamen differentiation, especially those for the morphological and functional differentiations of fertile stamens in non-model plants, await to be explored

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