Phenotypes of Floral Nectaries in Developmental Mutants of Legumes and What They May Tell about Genetic Control of Nectary Formation.

Abstract

Simple SummaryThe third largest angiosperm family, Leguminosae, is remarkable with the outstanding diversity of its flowers, usually monosymmetric and adapted to different pollination strategies. A key attractant of leguminous flowers is nectar. Compared with Arabidopsis (Brassicaceae), very little is known about regulation of floral nectaries development in legumes. This work aimed to investigate details of these nectaries’ morphology in flowers of mutants of different legume species. It was found that the changes in identity of petals and stamens usually do not affect a proper structure and position of nectaries in leguminous flowers, thus suggesting a high stability of attracting structures versus the pronounced plasticity of perianth and stamens. Some of genes involved in regulation of nectary development in Arabidopsis seem to have the same functions in legumes. The principal difference between Arabidopsis and legumes is connected with a flower monosymmetry in most representatives of the latter taxon, which is also reflected in structure of their floral nectaries.The vast majority of angiosperms attracts animal pollinators with the nectar secreted through specialized floral nectaries (FNs). Although there is evidence that principal patterns of regulation of FN development are conserved in large angiosperm clades, these structures are very diverse considering their morphology and position within a flower. Most data on genetic control of FN formation were obtained in surveys of a model plant species, Arabidopsis thaliana (Brassicaceae). There are almost no data on genetic factors affecting FN development in Leguminosae, the plant family of a high agricultural value and possessing outstandingly diverse flowers. In this work, the morphology of FNs was examined in a set of leguminous species, both wild-type and developmental mutants, by the means of a scanning electron microscopy. Unlike Brassicaceae, FNs in legumes are localized between stamens and a carpel instead of being associated with a certain floral organ. FNs were found stable in most cases of mutants when perianth and/or androecium morphology was affected. However, regulation of FN development by BLADE-ON-PETIOLE-like genes seems to be a shared feature between legumes (at least Pisum) and Arabidopsis. In some legumes, the adaxial developmental program (most probably CYCLOIDEA-mediated) suppresses the FN development. The obtained results neither confirm the role of orthologues of UNUSUAL FLORAL ORGANS and LEAFY in FN development in legumes nor reject it, as two studied pea mutants were homozygous at the weakest alleles of the corresponding loci and possessed FNs similar to those of wild-type.