MicroRNA and tasiRNA diversity in mature pollen of Arabidopsis thaliana.
BACKGROUND
New generation sequencing technology has allowed investigation of the small RNA populations of flowering plants at great depth. However, little is known about small RNAs in their reproductive cells, especially in post-meiotic cells of the gametophyte generation. Pollen - the male gametophyte - is the specialised haploid structure that generates and delivers the sperm cells to the female gametes at fertilisation. Whether development and differentiation of the male gametophyte depends on the action of microRNAs and trans-acting siRNAs guiding changes in gene expression is largely unknown. Here we have used 454 sequencing to survey the various small RNA populations present in mature pollen of Arabidopsis thaliana.


RESULTS
In this study we detected the presence of 33 different microRNA families in mature pollen and validated the expression levels of 17 selected miRNAs by Q-RT-PCR. The majority of the selected miRNAs showed pollen-enriched expression compared with leaves. Furthermore, we report for the first time the presence of trans-acting siRNAs in pollen. In addition to describing new patterns of expression for known small RNAs in each of these classes, we identified 7 putative novel microRNAs. One of these, ath-MIR2939, targets a pollen-specific F-box transcript and we demonstrate cleavage of its target mRNA in mature pollen.


CONCLUSIONS
Despite the apparent simplicity of the male gametophyte, comprising just two different cell types, pollen not only utilises many miRNAs and trans-acting siRNAs expressed in the somatic tissues but also expresses novel miRNAs.
Grant-Downton
Robert
R
Department of Plant Sciences, Oxford OX1, 3RB, UK. robert.grant-downton@plants.ox.ac.uk
Le Trionnaire
Gael
G
Schmid
Ralf
R
Rodriguez-Enriquez
Josefina
J
Hafidh
Said
S
Mehdi
Saher
S
Twell
David
D
Dickinson
Hugh
H
D017360:Arabidopsis / Q000235:genetics*; D001483:Base Sequence; D019295:Computational Biology; D018506:Gene Expression Regulation, Plant; D035683:MicroRNAs / Q000235:genetics*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011058:Pollen / Q000235:genetics*; D018749:RNA, Plant / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics*; D017423:Sequence Analysis, RNA
D035683:MicroRNAs; D018749:RNA, Plant; D034741:RNA, Small Interfering