DCL5

DICER-LIKE 5 (DCL5) is a plant Dicer-like endoribonuclease that functions in the biogenesis of 24-nucleotide reproductive phased small interfering RNAs (phasiRNAs). The gene is specific to monocots and plays a central role during early anther development, where these small RNAs accumulate at high levels.¹

DCL5 originated through duplication and functional specialization of DCL3, giving rise to a distinct small RNA pathway associated with plant reproduction.²

Phylogenetic analyses indicate that DCL5 arose early in monocot evolution, likely before the diversification of grasses, and is absent from most eudicots.³ Comparative genomics further places the origin of DCL5 at or before early-diverging monocots such as Acorus americanus, suggesting an ancient duplication event followed by lineage-specific retention.⁴

This duplication led to functional divergence between DCL3 and DCL5, with DCL3 primarily associated with heterochromatic siRNA pathways and DCL5 specialized for reproductive phasiRNA production in monocots.⁵

The diversification of DCL5 parallels the expansion and diversification of reproductive phasiRNA loci in monocots, indicating co-evolution of this enzyme with its small RNA substrates.³

DCL5 processes precursor transcripts into 24-nucleotide reproductive phasiRNAs that accumulate during premeiotic and meiotic stages of anther development.⁶ DCL5 specifically mediates the biogenesis of reproductive phasiRNAs, a subclass of phased small interfering RNAs enriched in premeiotic and meiotic anthers.⁶

These small RNAs are derived from PHAS precursor transcripts that are converted into double-stranded RNA and then processed into phased small interfering RNAs by DCL5.¹ In some nongrass monocots, many 24-nt reproductive phasiRNA precursors are predicted to form foldback or intramolecular duplex structures, indicating that DCL5-associated 24-nt reproductive phasiRNA biogenesis can proceed through more than one precursor structure or biogenesis pathway.⁷ In the canonical pathway, meiotic 24-nt reproductive phasiRNAs are triggered by the microRNA miR2275, which directs phased processing of precursor transcripts.⁸

Genetic and molecular studies in rice initially identified this monocot-specific Dicer protein (DCL3b, later renamed DCL5) responsible for 24-nt phasiRNA production, distinct from DCL4, which generates 21-nt phasiRNAs.⁸

Unlike DCL3, which processes RNA polymerase IV-derived transcripts, DCL5 acts primarily on transcripts generated by RNA polymerase II, reflecting mechanistic divergence between these pathways.⁵

DCL5 is essential for normal male reproductive development in grasses. Loss-of-function mutations in DCL5 lead to depletion of 24-nt reproductive phasiRNAs and defects in pollen development.¹ In maize and wheat, dcl5 mutants exhibit temperature-sensitive male sterility, indicating that the DCL5 pathway contributes to fertility under specific environmental conditions.¹⁹

Recent work suggests that some 24-nt reproductive phasiRNA biogenesis can occur independently of microRNA-directed cleavage and instead may involve conserved sequence motifs that guide DCL5-associated processing.⁹

These findings support a model in which DCL5-dependent phasiRNAs contribute to transcriptional regulation and developmental robustness during male gametophyte formation.