Poster: Plant-symbiont interactions

Abs # 580: A Medicago truncatula PIN gene with effects on nodulation

Presenter:	Huo, Xiuyan , xhuo@clemson.edu
Authors	Huo, Xiuyan  (A)   Schnabel, Elise  (A)   Frugoli, Julia  (A)
Affiliations:	(A): Clemson University

Medicago truncatula is a model legume used to study the molecular mechanisms underlying nodulation. Multiple lines of evidence suggest auxin plays a role in nodule development. Studies of polar auxin transport (PAT) in Arabidopsis have shown that PAT is in part mediated by auxin influx and efflux carriers. We report the cloning of ten PIN genes (auxin efflux carriers) in M. truncatula. We determined map positions for nine of these MtPIN genes. Sequence comparison of the MtPINs to Arabidopsis PIN genes and PIN genes from other species indicates that PIN genes share a common overall structure, with several areas of high homology between members of the gene family both within M. truncatula and across species boundaries. We used these conserved areas to construct a molecular phylogeny. Assignment of a direct correspondence between AtPINs and MtPINs is not possible based on sequence alone. M. truncatula has one more expressed PIN gene that Arabidopsis, and several PINs have no easily discernable ortholog. We have identified one putative direct ortholog; MtPIN2 is closest in sequence to AtPIN2, a root-specific PIN. RT-PCR analysis demonstrates that like AtPIN2, MtPIN2 is expressed only in root tissue. RNA interference constructs were used to generate transgenic M. truncatula roots lacking the expression of MtPIN genes. In the case of the MtPIN2 RNAi plants, the construct effectively eliminates the PIN2 message, but not the PIN1, PIN3 and PIN4 messages (testing for PIN 6-10 expression is underway). Initial cursory analysis of nodulation in MtPIN2 RNAi roots revealed fewer nodules than uninfected roots. Localization of MtPIN2 transcripts and protein is underway. RNAi cassettes for MtPIN1-4 have been constructed and will be used to transform roots.