The maize SBP-box transcription factor encoded by tasselsheath4 regulates bract development and the establishment of meristem boundaries

Abstract

Plant architecture consists of repeating units called phytomers, each containing an internode, leaf and axillary meristem. The formation of boundaries within the phytomer is necessary to differentiate and separate these three components, otherwise some will grow at the expense of others. The microRNA-targeted SBP-box transcription factor tasselsheath4 (tsh4) plays an essential role in establishing these boundaries within the inflorescence. tsh4 mutants display altered phyllotaxy, fewer lateral meristems and ectopic leaves that grow at the expense of the meristem. Double-mutant analyses of tsh4 and several highly branched mutants, such as ramosa1-3 and branched silkless1, demonstrated a requirement for tsh4 in branch meristem initiation and maintenance. TSH4 protein, however, was localized throughout the inflorescence stem and at the base of lateral meristems, but not within the meristem itself. Double labeling of TSH4 with the ramosa2, branched silkless1 and knotted1 meristem markers confirmed that TSH4 forms a boundary adjacent to all lateral meristems. Indeed, double labeling of miR156 showed a meristem-specific pattern complementary to that of TSH4, consistent with tsh4 being negatively regulated by this microRNA. Thus, downregulation of TSH4 by a combination of microRNAs and branching pathway genes allows the establishment of lateral meristems and the repression of leaf initiation, thereby playing a major role in defining meristem versus leaf boundaries.

Analysis of the barley bract suppression gene Trd1

“…In mutants of TASSEL SHEATH1 (Tsh1), the maize ortholog of Nl1, the bracts subtend branches and spikelet pairs in both in tassel and ear . Five Tsh genes affecting extra bract suppression have been identified in maize Chuck et al 2010). Apart from Tsh1, only Tsh4 has been cloned (Chuck et al 2010).…”

“…Five Tsh genes affecting extra bract suppression have been identified in maize Chuck et al 2010). Apart from Tsh1, only Tsh4 has been cloned (Chuck et al 2010). Trd1 was proposed as an ortholog of maize Tsh1 and rice Nl1 based on evidence from conservation of synteny, mRNA expression patterns and PCR-resequencing of two mutant and a non-related wild type alleles .…”

“…For maize, Whipple et al (2010) identified five separate genes that regulate bract development, Tsh1-Tsh5. In addition to Tsh1, Tsh4 has been cloned and identified as an SBP box transcription factor (Chuck et al 2010). In rice, two genes have been identified which suppress the development of the neck (collar) leaf phenotype, Nl1 and Nl2 (Khush 1987).…”

“…Alternatively it could be that these genes are yet to be identified in barley and rice. Tsh4 (Chuck et al 2010) is located on maize chromosome 5, and is not within a gene block that is a duplicate of the gene block containing Tsh1. In barley, four of the lines previously considered allelic to Trd1 based on past allelism tests produced the phenotype but did not contain a mutation in the coding DNA sequence.…”

Cloning and characterization of SPL-family genes in the peanut (Arachis hypogaea L.)

“…Furthermore, OsSPL14 (Miura et al, 2010) and OsSPL16 (Wang et al, 2012) play crucial roles in determining grain quality and yield in rice. tsh4 (tassel sheath4), a member of the maize SBP-box gene family, regulates bract development, and is required for branch meristem initiation and maintenance (Chuck et al, 2010). In addition, a series of studies have shown that SPLs play important roles in regulating plant developmental phase transition.…”