Gametogenesis in the Chlamydomonas reinhardtii minus mating type is controlled by two genes, MID and MTD1

Genetics. 2007 Jun;176(2):913-25. doi: 10.1534/genetics.106.066167. Epub 2007 Apr 15.

Abstract

In the unicellular algae Chlamydomonas reinhardtii, the plus and minus mating types are controlled by a complex locus, MT, where the dominant MID gene in the MT(-) locus has been shown to be necessary for expression of minus-specific gamete-specific genes in response to nitrogen depletion. We report studies on MID expression patterns during gametogenesis and on a second gene unique to the MT(-) locus, MTD1. Vegetative cells express basal levels of MID. An early activation of MID transcription after nitrogen removal, and its sequence similarity to plant RWP-RK proteins involved in nitrogen-responsive processes, suggest that Mid conformation/activity may be nitrogen sensitive. A second stage of MID upregulation correlates with the acquisition of mating ability in minus gametes. Knockdown of MTD1 by RNAi in minus strains results in a failure to differentiate into gametes of either mating type after nitrogen deprivation. We propose that intermediate Mid levels are sufficient to activate MTD1 transcription and to repress plus gamete-specific genes and that MTD1 expression in turn allows the threshold-level MID expression needed to turn on minus gamete-specific genes. We further propose that an MTD1-equivalent system, utilizing at least one gene product encoded in the MT(+) locus, is operant during plus gametogenesis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Algal Proteins / genetics*
  • Animals
  • Blotting, Northern
  • Cell Culture Techniques
  • Chlamydomonas reinhardtii / classification
  • Chlamydomonas reinhardtii / cytology
  • Chlamydomonas reinhardtii / genetics
  • Chlamydomonas reinhardtii / physiology*
  • Crosses, Genetic
  • DNA Primers
  • Gametogenesis / genetics*
  • Gene Expression Regulation*
  • Genes, Dominant
  • Membrane Glycoproteins / genetics*
  • Phylogeny
  • RNA / genetics
  • RNA / isolation & purification
  • Repressor Proteins / genetics*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Ribonucleases / metabolism
  • Trans-Activators / genetics*
  • Up-Regulation

Substances

  • Algal Proteins
  • DNA Primers
  • Membrane Glycoproteins
  • Repressor Proteins
  • Trans-Activators
  • RNA
  • Ribonucleases