Feminized tassels of maize mop1 and ts1 mutants exhibit altered levels of miR156 and specific SBP-box genes

Abstract

Development of the unisexual maize inflorescences requires the abortion of pistillate primordia in the florets of the developing tassel and the arrest of staminate primordia in the florets of the developing ears. Mutations of many genes that lie within this sexual differentiation pathway, such as tasselseed1 (ts1), or that influence this pathway, such as mediator of paramutation 1 (mop1), result in feminization of the normally male tassel. Here, we show the loss of mop1 or ts1 function results in increased mRNA levels for several members of the SBP-box gene family. Our analyses of this family expand the number of maize SBP-box genes from 9 to 31 members. Intron-exon structures as well as phylogenetic data support the division of these family members into six groups. The SBP-box genes upregulated in feminized tassels fall into two groups, share common structural motifs and include the presence of a target site for miR156. Small RNA blots show miR156 levels are decreased in both mop1 and ts1 mutants. While there is a correlation between miR156 levels and SBP-box gene transcript levels, this correlation is not absolute, and thus we hypothesize that decreased levels of miR156 may provide competency for SBP-box gene upregulation by other common factors yet to be identified. We present a model that provides a putative link between ts1, ts2, ts4, Ts6, and mop1 in the sex-determination pathway.

miR156-Targeted and Nontargeted SBP-Box Transcription Factors Act in Concert to Secure Male Fertility in Arabidopsis

“…Interesting in this context is that both miR156/7-targeted and nontargeted SBP-box genes, which according to our data regulate anther development similarly and as early as SPL/NZZ, are well conserved between monocots and dicots (Xie et al, 2006;Riese et al, 2007;Hultquist and Dorweiler, 2008). It would thus be interesting to determine if SBP-box genes play an evolutionarily more conserved role in sporogenesis.…”

RNA-mediated trans -communication can establish paramutation at the b1 locus in maize

“…In Arabidopsis, two miRNA species (20 and 21 nt) are observed for miR156 from shoot apices (37). In maize, a single miRNA species has been reported for miR156 (35,38), but its specific size was not reported. We found that similar to Arabidopsis, two size classes of miR156 can be observed in maize.…”

Ontogeny of the Maize Shoot Apical Meristem

“…As previously described, eight SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) transcripts targeted by the juvenile-stage regulatory RNA miR156 were upregulated in the L14 stage and lateral meristems (see Supplemental Data Set 14 online) (Chuck et al, 2007;Hultquist and Dorweiler, 2008;Strable et al, 2008). In addition, GLOSSY15 (GL15), an AP2-like transcription factor that promotes the adult leaf identity, is upregulated in 14-d-old seedlings (Evans et al, 1994;Moose and Sisco, 1996;Lauter et al, 2005).…”

“…A complex interactive network of phase-specific transcription factors and regulatory small RNAs regulate vegetative and reproductive phase change in plants (Moose and Sisco, 1996;Lauter et al, 2005;Chuck et al, 2007;Hultquist and Dorweiler, 2008). To examine the transcriptional differences among juvenilestage SAMs, adult-stage SAMs, and lateral shoot meristems from adult nodes on a genomic scale, the SAM and youngest leaf primordium were microdissected from L1-stage embryos and L14-stage seedlings, and lateral meristems were isolated from L14-stage seedlings.…”