Author:
Zhai Jixian,Zhang Han,Arikit Siwaret,Huang Kun,Nan Guo-Ling,Walbot Virginia,Meyers Blake C.
Abstract
Maize anthers, the male reproductive floral organs, express two classes of phased small-interfering RNAs (phasiRNAs). PhasiRNA precursors are transcribed by RNA polymerase II and map to low-copy, intergenic regions similar to PIWI-interacting RNAs (piRNAs) in mammalian testis. From 10 sequential cohorts of staged maize anthers plus mature pollen we find that 21-nt phased siRNAs from 463 loci appear abruptly after germinal and initial somatic cell fate specification and then diminish, whereas 24-nt phasiRNAs from 176 loci coordinately accumulate during meiosis and persist as anther somatic cells mature and haploid gametophytes differentiate into pollen. Male-sterileocl4anthers defective in epidermal signaling lack 21-nt phasiRNAs. Male-sterile mutants with subepidermal defects—mac1(excess meiocytes),ms23(defective pretapetal cells), andmsca1(no normal soma or meiocytes)—lack 24-nt phasiRNAs.ameiotic1mutants (normal soma, no meiosis) accumulate both 21-nt and 24-nt phasiRNAs, ruling out meiotic cells as a source or regulator of phasiRNA biogenesis. By in situ hybridization, miR2118 triggers of 21-nt phasiRNA biogenesis localize to epidermis; however, 21-PHASprecursors and 21-nt phasiRNAs are abundant subepidermally. The miR2275 trigger, 24-PHASprecursors, and 24-nt phasiRNAs all accumulate preferentially in tapetum and meiocytes. Therefore, each phasiRNA type exhibits independent spatiotemporal regulation with 21-nt premeiotic phasiRNAs dependent on epidermal and 24-nt meiotic phasiRNAs dependent on tapetal cell differentiation. Maize phasiRNAs and mammalian piRNAs illustrate putative convergent evolution of small RNAs in male reproduction.
Funder
National Science Foundation
Publisher
Proceedings of the National Academy of Sciences
Cited by
275 articles.
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