Pollen tube growth and guidance is regulated by POP2, an Arabidopsis gene that controls GABA levels.
During angiosperm reproduction, pollen grains form a tube that navigates through female tissues to the micropyle, delivering sperm to the egg; the signals that mediate this process are poorly understood. Here, we describe a role for gamma-amino butyric acid (GABA) in pollen tube growth and guidance. In vitro, GABA stimulates pollen tube growth, although vast excesses are inhibitory. The Arabidopsis POP2 gene encodes a transaminase that degrades GABA and contributes to the formation of a gradient leading up to the micropyle. pop2 flowers accumulate GABA, and the growth of many pop2 pollen tubes is arrested, consistent with their in vitro GABA hypersensitivity. Some pop2 tubes continue to grow toward ovules, yet they are misguided, presumably because they target ectopic GABA on the ovule surface. Interestingly, wild-type tubes exhibit normal growth and guidance in pop2 pistils, perhaps by degrading excess GABA and sharpening the gradient leading to the micropyle.
Palanivelu
Ravishankar
R
Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA.
Brass
Laura
L
Edlund
Anna F
AF
Preuss
Daphne
D
D017360:Arabidopsis / Q000166:cytology / Q000235:genetics* / Q000254:growth & development*; D029681:Arabidopsis Proteins; D005306:Fertilization / Q000235:genetics*; D035264:Flowers / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D006133:Growth Substances / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D000637:Transaminases / Q000378:metabolism; D014157:Transcription Factors / Q000172:deficiency* / Q000235:genetics; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D029681:Arabidopsis Proteins; D006133:Growth Substances; D014157:Transcription Factors; D005680:gamma-Aminobutyric Acid; D000637:Transaminases; C489779:POP2 protein, Arabidopsis