ALBERT, VICTOR A.1* and RICHARD W. JOBSON1,2. 1Biodiversity and Systematics, Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL 35487-0345; 2Department of Botany, The University of Queensland, Brisbane, QLD 4072, Australia. - Relaxed structural constraints in Utricularia (Lentibulariaceae): a possible basis in one or few genes regulating polar auxin transport.
Lloyd (1942) documented the unusual embryogeny of Utricularia,
a morphologically and ecologically diverse genus of carnivorous plants
in the Lentibulariaceae (Lamiales). Specifically, the traits of
apparent rootlessness (or retention of an aborted primary root),
asymmetrical phyllotaxis, and production of pin-like, anisophyllous
stems are suggestive of systemically altered regulation of polar auxin
transport. For example, mutants of the MONOPTEROS gene in
Arabidopsis are impaired in polar auxin transport, lack a
primary root, may have profound phyllotactic asymmetry, and may
produce inflorescence stems devoid of appendicular structures.
Mutations in other auxin-involved Arabidopsis genes are known
to produce pin-like inflorescences, and blockage of leaf organogenesis
in tomato through chemical inhibition of polar auxin transport can be
reversed by microapplication of auxin to the shoot tip. The embryonic
developmental problems of MONOPTEROS and similar mutants have
been ascribed to inhibition of an apical-basal auxin signal, whereas
the later effects on phyllotaxis (which include pin production) have
been attributed to disrupted radial auxin regulation.
Utricularia plants may represent naturally occurring polar
auxin transport mutants, and the resulting pleiotropic alterations of
the typical angiosperm body plan may have provided reduced selection
pressure for individuals with diverse morphologies to establish
founder populations and diverge. The possibility of a narrow genetic
basis for Utricularia vegetative diversity impacts the
interpretation of significantly higher molecular rates observed for
Utricularia plus Genlisea versus their sister clade,
Pinguicula, among seven loci spanning all three genomic
compartments (see abstract by Jobson and Albert, Botany2001).
Key words: Arabidopsis, auxin, development, Lentibulariaceae, molecular evolution