Perturbation of pheromone signaling modulates not only mating but also virulence in Cryptococcus neoformans, an opportunistic human pathogen known to encode three G␣, one G␤, and two G␥ subunit proteins. We have found that G␣s Gpa2 and Gpa3 exhibit shared and distinct roles in regulating pheromone responses and mating. Gpa2 interacted with the pheromone receptor homolog Ste3␣, G␤ subunit Gpb1, and RGS protein Crg1. Crg1 also exhibited in vitro GAP activity toward Gpa2. These findings suggest that Gpa2 regulates mating through a conserved signaling mechanism. Moreover, we found that G␥s Gpg1 and Gpg2 both regulate pheromone responses and mating. gpg1 mutants were attenuated in mating, and gpg2 mutants were sterile. Finally, although gpa2, gpa3, gpg1, gpg2, and gpg1 gpg2 mutants were fully virulent, gpa2 gpa3 mutants were attenuated for virulence in a murine model. Our study reveals a conserved but distinct signaling mechanism by two G␣, one G␤, and two G␥ proteins for pheromone responses, mating, and virulence in Cryptococcus neoformans, and it also reiterates that the link between mating and virulence is not due to mating per se but rather to certain mating-pathway components that encode additional functions promoting virulence. INTRODUCTIONCryptococcus neoformans is an encapsulated yeast-like fungus capable of infecting both immunocompromised and healthy individuals to cause life-threatening meningoencephalitis (Mitchell and Perfect, 1995;Chayakulkeeree and Perfect, 2006). The organism belongs to basidiomycota taxonomically and has a defined life cycle and a bipolar mating system with MAT␣ being the predominant mating type in both environmental and clinical settings (Hull and Heitman, 2002;Wang and Fox, 2005;Nielsen and Heitman, 2007). Like other fungi and higher eukaryotes, heterotrimeric G protein-mediated signaling pathways are central for C. neoformans to sense environmental-and host-imposed cues and to respond through regulation of developmental processes such as mating and haploid differentiation, as well as the production of several virulence factors including melanin and capsule (Alspaugh et al., 1998;Wang and Fox, 2005).The lower eukaryotic organisms such as fungi also encode multiple G␣ subunits, similar to higher eukaryotic organisms such as animals and plants . For example, the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe encode two G␣ subunits, the plant pathogen Ustilago maydis encodes four G␣ subunits, and many other fungal species contain three G␣ subunits. The S. cerevisiae G␣ Gpa1 is a negative regulator of the pheromone-responsive mating pathway (Whiteway et al., 1989;Whiteway et al., 1990;Clark et al., 1993;Kü bler et al., 1997;Colombo et al., 1998;Thevelein and Winde, 1999), whereas G␣ Gpa2 positively controls a glucose-sensing cAMP pathway for pseudohyphal differentiation and invasive growth (Kü bler et al., 1997;Lorenz and Heitman, 1997). Distinct, but largely similar, signaling pathways mediated by two G␣ subunits were also found in S. pombe (Sti...

Bidens frondosa L. (Asteraceae) is a widespread invasive weed in China. By experimental observation and bagging treatment, the reproductive biological characteristics of this species, such as phenology of flowering, floral syndrome, breeding system and seed germination characteristics, were studied to assess the association of these reproductive characteristics with invasiveness. Flowers of B. frondosa bloom from September to October every year in Ji'an city, Jiangxi province. The lifespan of a single capitulum is approximately 4 to 5 days, with 30 to 60 florets per capitulum. The capitulum diameter, anthocaulus length, floret length and width, stamen length and pistil length were 6.1, 30.9, 2.2, 0.6, 3.0 and 2.7 mm, respectively. The seed set percentage of 48.5% in the treatment of bagging flowers without emasculation suggests B. frondosa is self-compatible; meanwhile, the percentage of 63.1% in the treatment of bagging with emasculation and manual xenogamy suggests it also is cross-compatible. P/O ratio per capitulum of this species was 450.5, which suggests that the breeding system of B. frondosa is facultative xenogamous, and it needs pollinators to some degree. The main floral visitors were insects of Hymenoptera, Diptera and Lepidoptera. The 1000-achenes weight was 1.97 g. The achenes emerged as a small germination peak from the fourth to fifth day, and had a high accumulated germination rate of up to 84.0% on day 20 after sowing. Our experimental findings suggested that the reproductive biological characteristics, such as the versatile mating system of self-and cross-pollination, high seed production, a special method of achene dispersal and germination peak, accompanied by a high accumulated germination rate, might contribute to the invasive ability of B. frondosa.