The Walbot Lab has intriguing clues that a novel type of small RNA (phasiRNAs = phased small RNAs of 21 or 24 nucleotides) are critical for early steps in in anther development. PHAS loci are non repetitive, transcribed by RNA Pol II but do not encode proteins; the long non-coding transcript is processed into precisely the same 21 or 24 nt pieces by the binding of a 22 nt trigger molecule and the action of a specific Dicers (DCL4 for the 21 nt type and DCL5 for the 24 nt class). Only grass anthers produce the 24 nt phasiRNAs, and in maize they appear shortly before the start of meiosis. Based on current evidence, we hypothesize that epidermal cells make the 21 nt phasiRNAs and the archesporial cells make the 24 nt phasiRNAs. Genetic and molecular approaches are being used to discover the functions of these fascinating small molecules.
Bio-X Affiliated Faculty