PIN6, an auxin efflux transporter, is essential for nectar secretion in Arabidopsis thaliana.

Abstract

Nectar plays a vital role in plant reproductive success by attracting pollinators. Although much is known about the structural aspects of nectaries as well as the chemical composition of nectar from a host of species, there is little understanding on how a plant controls its nectar phenotype at a molecular level. Plant hormones, such as jasmonic acid, gibberellic acid, and auxin, are essential for proper development and their influence on nectar secretion was the focus of some early studies, but produced conflicting results. With our group’s identification of auxin-related genes preferentially expressed in Arabidopsis thaliana nectaries, it became clear that auxin might have an important role in regulating nectar secretion in the Brassicaceae. For example, multiple mutants for an irregular auxin efflux protein, PIN6, from Arabidopsis thaliana were identified. Distinct phenotypes and nectar outputs were identified with the various PIN6 mutants, including a mutant with a 30% increase in nectar sugar output (pin6-1) and a mutant with trace nectar sugar output (pin6-2). A positive correlation of nectar volume with PIN6 gene expression was found. Additionally, Arabidopsis thaliana, Brassica rapa, and various other flowers were cultured in solutions containing auxin and auxin transport inhibitors to determine auxin’s influence on nectar production in these species. PIN6 is essential for nectar secretion in A. thaliana and proper cellular auxin transport is needed to maintain typical nectar volumes, as well as for the expression of multiple key auxin genes. Manipulation of local auxin concentrations in the nectaries could potentially lead to the development of plants with traits that increase attractiveness to pollinators.