Reproductive phasiRNAs are the piRNAs of plants

Area of Science:

• Molecular Biology
• Genetics
• Developmental Biology

Background:

• Small RNAs are crucial for gene expression regulation, particularly in reproduction.
• Animal PIWI-interacting RNAs (piRNAs) and plant reproductive phased small interfering RNAs (phasiRNAs) are specialized small RNA classes with vital reproductive roles.
• These small RNA pathways have evolved independently in animals and plants.

Purpose of the Study:

• To compare the biogenesis, function, and evolutionary strategies of animal piRNAs and plant reproductive phasiRNAs.
• To identify similarities and differences between these two small RNA systems.
• To highlight unresolved questions regarding their molecular targets, functions, and evolutionary pressures.

Main Methods:

• Comparative review of existing literature on piRNA and phasiRNA pathways.
• Analysis of small RNA biogenesis mechanisms, including Dicer-dependence and PIWI-clade protein involvement.
• Examination of known and putative functions, including transposon silencing and roles in reproduction.

Main Results:

• Both piRNAs and phasiRNAs originate from Pol II-transcribed precursors but exhibit distinct biogenesis pathways.
• piRNA processing in metazoans is Dicer-independent with PIWI-clade protein amplification.
• Reproductive phasiRNAs are Dicer-dependent, initiated by miRNA-guided cleavage.

Conclusions:

• Despite distinct evolutionary paths, piRNAs and phasiRNAs share functional similarities in reproduction, suggesting convergent evolution.
• Key questions remain regarding the non-transposon targets of piRNAs and the functions of most reproductive phasiRNAs.
• Further research is needed to understand the molecular targets, diverse functions, and evolutionary drivers of these critical small RNA systems.