Isolation and characterisation of an <Emphasis Type="Italic">HpSHP</Emphasis> gene from <Emphasis Type="Italic">Hosta plantaginea</Emphasis>

Based on genetic and molecular analyses, the ABC model has been proposed to explain the genetic control of floral development. C-class MADS-box genes play crucial roles in Arabidopsis thaliana development by regulating the organ identities of stamens and gynoecium. The present research reports for the first time the cloning of an HpSHP gene from Hosta plantaginea (Lam.) Aschers. Phylogenetic analysis shows that HpSHP is a member of the C-class MADS-box genes that is closely related to C-lineage SHP homologues from monocot species. Semi-quantitative and real-time polymerase chain reaction analyses show that HpSHP expression is stamen and gynoecium specific. HpSHP also has spatial and temporal expression patterns in the reproductive organs of H. plantaginea. A functional analysis is carried out in Arabidopsis by overexpression of HpSHP. Homeotic transformations of sepals into carpelloid organs, bent ovaries, and prematurely shattering fruits are observed in 35S::HpSHP transgenic plants. All these results show that HpSHP plays a crucial role in gynoecium development.     

Differentiating Arabidopsis Shoots from Leaves by Combined YABBY Activities

In seed plants, leaves are born on radial shoots, but unlike shoots, they are determinate dorsiventral organs made of flat lamina. YABBY genes are found only in seed plants and in all cases studied are expressed primarily in lateral organs and in a polar manner. Despite their simple expression, Arabidopsis thaliana plants lacking all YABBY gene activities have a wide range of morphological defects in all lateral organs as well as the shoot apical meristem (SAM). Here, we show that leaves lacking all YABBY activities are initiated as dorsiventral appendages but fail to properly activate lamina programs. In particular, the activation of most CINCINNATA-class TCP genes does not commence, SAM-specific programs are reactivated, and a marginal leaf domain is not established. Altered distribution of auxin signaling and the auxin efflux carrier PIN1, highly reduced venation, initiation of multiple cotyledons, and gradual loss of the SAM accompany these defects. We suggest that YABBY functions were recruited to mold modified shoot systems into flat plant appendages by translating organ polarity into lamina-specific programs that include marginal auxin flow and activation of a maturation schedule directing determinate growth.     

Polar auxin transport together with AINTEGUMENTA and REVOLUTA coordinate early Arabidopsis gynoecium development

In flowering plants the gynoecium is the female reproductive structure and the site of oogenesis, fertilization, and maturation of the embryo and the seed. Proper development of the gynoecium requires that the early gynoecial primordium be partitioned into distinct spatial domains with divergent fates. Regulated transport of the phytohormone auxin previously has been shown to play a role in the patterning of spatial domains along the apical-basal axis of the gynoecium. Here we establish a role for auxin transport in patterning along the medio-lateral axis of the gynoecial ovary. We demonstrate that auxin transport is required for the development of the medial ovary domain that contains the carpel margin meristem, a vital female reproductive structure. Disruptions in auxin transport enhance the medial domain defects observed in aintegumenta and revoluta mutant genotypes. AINTEGUMENTA and REVOLUTA are likely to function in parallel and partially overlapping pathways required for medial domain development. Our data indicate that different ovary domains are differentially sensitive to the reduction of polar auxin transport and the loss of AINTEGUMENTA and REVOLUTA activity. We suggest that an auxin-mediated positional cue is important for the differential specification of the medial and lateral ovary domains.     

LjABCB1, an ATP-binding cassette protein specifically induced in uninfected cells of Lotus japonicus nodules

Legume plants develop root nodules through symbiosis with rhizobia, and fix atmospheric nitrogen in this symbiotic organ. Development of root nodules is regulated by many metabolites including phytohormones. Previously, we reported that auxin is strongly involved in the development of the nodule vascular bundle and lenticel formation on the nodules of Lotus japonicus. Here we show that an ATP-binding cassette (ABC) protein, LjABCB1, which is a homologue of Arabidopsis auxin transporter AtABCB4, is specifically expressed during nodulation of L. japonicus. A reporter gene analysis indicated that the expression of LjABCB1 was restricted to uninfected cells adjacent to infected cells in the nodule, while no expression was observed in shoot apical meristems or root tips, in which most auxin transporter genes are expressed. The auxin transport activity of LjABCB1 was confirmed using a heterologous expression system.