Table 1.

Parallels between grass phasiRNAs and mammalian piRNAs

Characteristic	Grass (maize) phasiRNA*		Mammalian piRNA†
Organ	Anther		Testis
Developmental stage	Premeiotic	Meiotic	Prepachytene	Pachytene
Peak timing	0.4-mm anther	2.0-mm anther	12.5 dpp	17.5 dpp
Size	21 nt	24 nt	26–27 nt	29–30 nt
AGO partner	AGO5c‡	AGO18b‡	MILI, MIWI2	MIWI
Master regulator	miR2118	miR2275	Unknown	A-myb
Number of loci	463	176	∼900	∼100
Abundance	Very high
Distribution	Present on all chromosomes; most loci are clustered
Precursor	Noncoding, Pol II transcripts
Single copy?	Nearly all
Repeat associated?	Few
Impacts on fertility	Misregulated in sterile mutants; biogenesis defects can cause sterility
Targeting	The majority lack complementarity to TEs or other loci
Function(s)	Unknown		Mainly unknown; a subset silence TEs

^*Properties of phasiRNAs are from this study and prior reports (8, 9, 11).

^†Mammalian piRNAs have been extensively characterized (1, 2, 4, 5).

^‡Proposed binding partners.