Regulation of arbuscule degeneration during arbuscular mycorrhizal symbiosis
M. HARRISON (1), D. Floss (2), K. Bhattarai (2), S. Gomez (2), H. Park (2), A. MacLean (2), V. Levesque-Tremblay (2) (1) Boyce Thompson Institute, Cornell University, U.S.A.; (2) Boyce Thompson Institute, U.S.A.

Most vascular flowering plants have the capacity to form mutualistic symbioses with arbuscular mycorrhizal (AM) fungi. The associations develop in the roots where the fungus colonizes the cortex and develops branched hyphae, called arbuscules, in the cortical cells. Arbuscule development requires the coordinate differentiation of both symbionts. Each intracellular hypha undergoes terminal differentiation to form an arbuscule and this developmental process is coordinated with cellular reorganization of the cortex cell including the deposition of the periarbuscular membrane which envelops the arbuscule.  Arbuscules have a finite life and after several days, they undergo a degeneration process, in which they collapse and eventually disappear from the cell. Currently, our understanding of this process is relatively limited, although it is clear that phosphate transporters functioning in the periarbuscular membrane influence arbuscule lifespan. Through analysis of a M. truncatula mtpt4 mutant, in which arbuscules degenerate prematurely, we defined a set of M. truncatula genes whose expression is enhanced during arbuscule degeneration. Expression of these  so called ‘ degeneration program genes’ is induced by expression of a Myb transcription factor and in mtpt4 myb double mutants, premature arbuscule degeneration is partially suppressed, suggesting that Myb plays a role in triggering arbuscule degeneration. Consistent with this, overexpression of Myb impairs development of symbiosis. Protein interaction studies and analyses of mutants indicate that Myb acts in concert with one or more GRAS proteins to regulate transcription of an arbuscule degeneration program. These data and further progress to elucidate the mechanisms underlying arbuscule degeneration will be presented.

Abstract Number: C13-5, P2-62
Session Type: Concurrent