Higher plants display a variety of architectures that are defined by the degree of branching, internodal elongation, and shoot determinancy. Studies on the model plants of Arabidopsis thaliana and tomato and on crop plants such as rice and maize have greatly strengthened our understanding on the molecular genetic bases of plant architecture, one of the hottest areas in plant developmental biology. The identification of mutants that are defective in plant architecture and characterization of the corresponding and related genes will eventually enable us to elucidate the molecular mechanisms underlying plant architecture. The achievements made so far in studying plant architecture have already allowed us to pave a way for optimizing the plant architecture of crops by molecular design and improving grain productivity.

Molecular Basis of Plant Architecture

Biologists were puzzled by the discovery of left-handed Z-DNA because it seemed unnecessary. Z-DNA was stabilized by the negative supercoiling generated by transcription, which indicated a transient localized conformational change. Few laboratories worked on the biology of Z-DNA. However, the discovery that certain classes of proteins bound to Z-DNA with high affinity and great specificity indicated a biological role. The most recent data show that some of these proteins participate in the pathology of poxviruses.

Z-DNA: the long road to biological function

Phylogenetic analyses of angiosperm MADS-box genes suggest that this gene family has undergone multiple duplication events followed by sequence divergence. To determine when such events have taken place and to understand the relationships of particular MADS-box gene lineages, we have identified APETALA1/FRUITFULL-like MADS-box genes from a variety of angiosperm species. Our phylogenetic analyses show two gene clades within the core eudicots, euAP1 (including Arabidopsis APETALA1 and Antirrhinum SQUAMOSA) and euFUL (including Arabidopsis FRUITFULL). Non-core eudicot species have only sequences similar to euFUL genes (FUL-like). The predicted protein products of euFUL and FUL-like genes share a conserved C-terminal motif. In contrast, predicted products of members of the euAP1 gene clade contain a different C terminus that includes an acidic transcription activation domain and a farnesylation signal. Sequence analyses indicate that the euAP1 amino acid motifs may have arisen via a translational frameshift from the euFUL/FUL-like motif. The euAP1 gene clade includes key regulators of floral development that have been implicated in the specification of perianth identity. However, the presence of euAP1 genes only in core eudicots suggests that there may have been changes in mechanisms of floral development that are correlated with the fixation of floral structure seen in this clade.

https://www.genetics.org/content/genetics/165/2/821.full.pdf

Duplication and diversification in the APETALA1/FRUITFULL floral homeotic gene lineage: implications for the evolution of floral development.

The two recent theories of flowering plant evolutionary origins—the Anthophyte and Neo-Pseudanthial theories—are based on phylogenies (from morphological data) that show Gnetales as extant sister to angiosperms or as paraphyletic to angiosperms. Gnetales figured prominently in homology assessments and evolutionary scenarios of these theories. Several recent studies, including ours, provide strong evidence that extant gymnosperms are monophyletic, so Gnetales are most closely related to other gymnosperms, not to flowering plants. This removes the basis for both recent theories, leaving earlier theories that relate flowering plants to fossil “seed-fern” gymnosperms as the only active contenders. Our data from the homeotic gene Floricaula/LEAFY imply that the lineage leading to flowering plants originally had two copies of this gene, but that one copy was lost in flowering plants, which suggests a new theory: that developmental control of flower organization derives more from systems active in the m...

https://bioone.org/journals/systematic-botany/volume-25/issue-2/2666635/The-Mostly-Male-Theory-of-Flower-Evolutionary-Origins--from/10.2307/2666635.pdf

The Mostly Male Theory of Flower Evolutionary Origins: from Genes to Fossils

Floral Initiation and Inflorescence Architecture: A Comparative View

In angiosperms, the formation of the flower meristem is controlled by partially redundant flower meristem identity genes of which FLORICAULA (FLO)/LEAFY (LFY ) plays a central role. It is not known whether formation of reproductive organs of pre-angiosperm species is similarly regulated. Recently, a FLO/LFY-like cDNA, NEEDLY (NLY ), has been cloned in a conifer species Pinus radiata (D. Don). Here we report cloning of a different P
inus
radiata F
LO/L
FY-l ike cDNA, PRFLL. PRFLL had two large regions of high similarity to angiosperm FLO/LFY orthologues: amino acids 61–126 and 247–406 (50% and 81% identity, and 75% and 88% similarity, respectively, to LFY) and shorter regions of local similarity. Overall identity was 53% to LFY and 61% to NLY. Phylogenetic analysis of deduced protein sequences including partial LFY-like sequences from Pseudotsuga menziesii indicated that conifer proteins constituted a separate clade that could be divided into two groups represented by NLY and PRFLL. In contrast to angiosperms, both conifers had two paralogous proteins resembling LFY. Northern hybridisation analysis revealed expression of PRFLL in vegetative buds of juvenile, adolescent and mature trees. The transcript was not detected in vascular cambium, roots or secondary needles. To follow PRFLL expression during the early stages of cone development we analysed a temporal series of buds containing cone primordia, and developing cones, using Northern hybridisation and confocal microscopy in parallel. PRFLL mRNA was detected in buds from dominant and subordinate branches, in which cone and shoot primordia develop, and in developing male cones but not in developing female cones. Expression was particularly high in buds containing axillary primordia prior to their differentiation as male cone primordia. This is consistent with PRFLL being involved in determination of the male cone primordium identity.

Adrian Walden

Papers

PRFLL – a Pinus radiata homologue of FLORICAULA and LEAFY is expressed in buds containing vegetative shoot and undifferentiated male cone primordia