The peptidyl-prolyl isomerases FKBP15-1 and FKBP15-2 negatively regulate lateral root development by repressing a vacuolar invertase in Arabidopsis

Background Lateral root (LR) architecture determines the efficiency of nutrient absorption and anchors the plant. Internal auxin regulatory mechanisms that control the development of LR have been identified, but how external nutrients influence lateral root development remains elusive. Results We have characterized the functions of the FK506-binding proteins FKBP15-1 and FKBP15-2 in Arabidopsis. FKBP genes are mainly expressed in the vascular bundle of the root basal meristem region, and the FKBP proteins are localized to the endoplasmic reticulum. Co-IP and BIFC assays showed that FKBP15-1 and FKBP15-2 interact with the vacuolar invertase 2 (VIN2). Compared to Col-0 and the single mutants, the double mutant fkbp15-1fkbp15-2 had more LRs and LR initiation density, and possessed higher sucrose catalytic activity. Moreover, VIN2 can complement the phenotype of increased LRs in the fkbp15-1fkbp15-2 double mutant. Conclusion Our results indicate that FKBP15-1 and FKBP15-2 together participate in the control of LR numbers by regulating the enzyme activity of VIN2. Due to the activity of peptidylprolyl cis-trans isomerases owned by FKBP family proteins, our results provide a clue to further analysis the interplay between lateral root development and protein modification.

QUANTITATIVE ASSESSMENT OF ANISOCOTYLY IN HABERLEA RHODOPENSIS AND RAMONDA MYCONI

Anisocotyly, the unequal development of cotyledons post germination, is a unique trait observed only in Old World Gesneriaceae (Lamiales). New World Gesneriaceae have isocotylous seedlings. In both Old and New World Gesneriaceae, cotyledons initially grow equally for a short period just after germination. In the New World species, both cotyledons cease their growth at the same time early on, whereas in Old World species one cotyledon continues to expand to become a macrocotyledon while the other withers away. In this study, cotyledon growth was observed in two European Old World Gesneriaceae: Haberlea rhodopensis and Ramonda myconi. The results were compared with those for the typical anisocotylous species Streptocarpus rexii and the typical isocotylous species Corytoplectus speciosus. We found that the cotyledon growth patterns in Haberlea rhodopensis and Ramonda myconi were intermediate between the typical anisocotylous or isocotylous species. Haberlea rhodopensis and Ramonda myconi showed irregular growth patterns, with some plants being slightly anisocotylous but most being isocotylous. The developmental basis for the residual anisocotyly, the extended basal meristem activity in the macrocotyledon, appeared to be identical in the European species to that in the typical Old World Streptocarpus rexii but weakly expressed, rare and terminated early. In conclusion, European Gesneriaceae retain a reduced anisocotylous growth that may be linked to their early plumule development.

Aspects of inflorescence and floral development in the putative basal angiosperm Amborella trichopoda (Amborellaceae)

Amborella has woody axes whose development is intrinsically plagiotropic and determinate. The tree habit is achieved through overtopping of older axes by basally produced younger axes, as in Mangenot's model. Inflorescence units, which are produced in the axils of distal leaves, may be described as extended cymes, each branch ending in a flower. Basal bracteoles have a decussate arrangement, which is modified to an alternate phyllotaxis distally. Flowers produce one or more additional bracteoles with a rapid transition to the spiral phyllotaxis of the broad overlapping tepals. In this transition the initially conical floral apex becomes invaginated to form a floral cup, with subsequent appendages appearing on its inner margin. The floral apex then forms the flat base of the cup but retains a discrete single tunica layer. The receptacular bowl is deepened and narrowed by the basal meristem of each appendage, the last formed floral organs usually consuming the floral meristem. Sexual parts are more numerous in male than female flowers, accounting for their size difference, but primordia of stamens and carpels are initially very similar. Floral symmetry is largely a consequence of close packing of appendages within the floral cup. In its initial stages of development the flower does not conform to any conventional floral model in angiosperms and is better regarded as highly specialized rather than ancestral in its synorganization. This is not unexpected in a lineage of such long independent evolution.Key words: Amborella, basal angiosperm, development, inflorescence, primitive flower.