(American Journal of Botany. ;91:0.)
© Botanical Society of America, Inc.
MADS-box genes and the basal-most angiosperm
Kim et al. examined gene structure and phylogeny of B-function MADS-box genes to provide additional evidence to support the basal-most status of Amborella among angiosperms. In particular, the AP3- and PI-homologues of Amborella, Am.tr.AP3 and Am.tr.PI, share several amino acid strings, including a prominent DEAER motif in the C-terminal domain, the most variable transcribed region. Duplication time of two major lineages of B-function genes was estimated to be ca. 260 million years ago, placing the duplication after the split between extant gymnosperms and angiosperms, but well before the oldest angiosperm fossils.
(see p. 2102)
Lolium perenne, a common perennial grass widely used for forage and turf, is often host to a fungal endophyte growing between its leaf cells. In Cheplick's study of endophyte infection on host recovery from severe drought stress, uninfected plants, both drought-stressed and controls produced more tillers, and greater leaf area and mass, than did infected plants. Although the grass=nendophyte symbiosis is mutualistic in other well-studied host=nfungus pairs, the relationship between L. perenne and its endophyte may primarily benefit the fungus, while being detrimental to the host under certain environmental conditions.
(see p. 1960)
The Little Aguja Pondweed (Potamogeton clystocarpus) is restricted to a single drainage in west Texas, where it is nearly morphologically indistinguishable from two more widespread pondweed species. Whittall et al. used AFLPs and DNA sequences from the nuclear and chloroplast genome to examine the degree of genetic distinctiveness, hybridization, and clonality in this endangered pondweed community. Seventy-seven percent of the AFLP variation separates P. clystocarpus from its sister species. Hybrids were only detected between the widespread species and clonality remained localized to individual pools. These results indicate P. clystocarpus is a genetically distinct cryptic species.
(see p. 1960)
In the vast majority of taxa with unisexual flowers, male and female flowers differ significantly in size. Most literature on this topic has focused on adaptive explanations for sexual size dimorphism. In Solanum, however, Diggle and Miller found that size differences between flower types are due to floral architecture; that is, the different flower types are spatially segregated within inflorescences, and location greatly affects flower size, irrespective of sexual function. Thus, in Solanum, architectural effects mimic sexual size dimorphism. To the extent that spatial segregation of flower types is common among taxa with unisexual flowers, such architectural "mimicry" may underlie other cases of sexual dimorphism.
(see p. 2024)
