MISSING FLOWERS gene controls axillary meristems initiation in sunflower

Abstract

The initiation and growth of axillary meristems are fundamental components of plant architecture. Here, we describe the mutant missing flowers (mf) of Helianthus annuus characterized by the lack of axillary shoots. Decapitation experiments and histological analysis indicate that this phenotype is the result of a defect in axillary meristem initiation. In addition to shoot branching, mutation affects floral differentiation. The indeterminate inflorescence of sunflower (capitulum) is formed of a large flat meristem which produces floret primordia in multiple spirals. In wildtype plants a bisecting crease divides each primordium in two distinct bumps that adopt different fate. The peripheral (abaxial) part of the primordium becomes a small leaf-like bract and the adaxial part becomes a flower. In the mf mutant, the formation of flowers at the axil of bracts is precluded. Histological analyses show that in floret primordia of the mutant a clear subdivision in dyads is not established. The primordia progressively bend inside and only large involucral floral bracts are developed. The results suggest that the MISSING FLOWERS gene is essential to provide or perceive an appropriate signal to the initiation of axillary meristems during both vegetative and reproductive phases.

Something on the Side: Axillary Meristems and Plant Development

“…The early stages of development of these two lateral meristem types are similar, as are the expression patterns of key genes, supporting the proposed homology in these structures (Long and Barton, 2000). Further evidence for this comes from a sunflower (Helianthus annus) mutant, missing flowers (mf), which lacks all AM and FMs, but which still possesses leaves and bracts (Fambrini et al, 2003), suggesting one gene product can control production of both structures. Much has been written about the nature of FMs (see, for instance, Zik and Irish, 2003), and they will not be discussed in detail in this review.…”

“…However, it has not yet been shown exactly how the Blind protein works to promote AM formation. The phenotype of the blind/torosa mutants is quite similar to the sunflower mutant missing flowers (Fambrini et al, 2003), described in Section 2. The affected gene has not been cloned, but it is possible that it is an orthologue of BLIND, or at least is involved in the same process.…”

Floral meristem initiation and emergence in plants

“…The missing flowers mutant lacks the adaxial domain and only bracts differentiate [102]. This Floral meristem initiation and emergence 3813…”

“…Calendula officianalis has a similar floret primordium organization, where bracts are absent and the floret primordium generates solely floret fate [102]. Bract suppression mediated by TASSEL SHEATH1 (TSH1) in maize and its orthologues NECK LEAF1 (NL1) in rice [103] and THIRD OUTER GLUME (TRD) in barley [104] shows functional conservation of bract regulation across the grass family.…”

A GRAS‐like gene of sunflower (Helianthus annuus L.) alters the gibberellin content and axillary meristem outgrowth in transgenic Arabidopsis plants

“…Furthermore, the genetic defect of Ls homologous also determines different plant architecture in monocots. In fact, loss of MONOCULM 1 (MOC1) function in rice results in lack of tillers as well as reduction of reproductive rachis branches and spikelets (Li et al 2003), suggesting that the floral meristem is a modified AM (Fambrini et al 2003;Bennet & Leyser 2006). The GRAS name was derived from the first three functionally characterised genes, GIBBERELLIN INSENSITIVE (GAI), REPRESSOR of ga1-3 (RGA) and SCARECROW (SCR) (Di Laurenzio et al 1996;Silverstone et al 1998;Pysh et al 1999).…”