Role of expansins in the rhizobia-legume symbiosis

BOGINO, P., BANCHIO, E., RIVELLI ANTONELLI, J., RINAUDI, L. Y GIORDANO, W

San Luis

Congreso; XXII Reunión anual de la Sociedad de Biología de Cuyo; 2004

Sociedad de Biología de Cuyo

Many legumes respond to rhizobia inoculation by developing new organs known as root nodules. Among the cell wall proteins studied to date, expansins are unique in their ability to induce immediate cell wall extension in vitro and cell expansion in vivo. This capacity to extend the cell wall is lost upon denaturation of wall protein. Gene expression analyses with gene specific probes have shown that expansin genes are differentially regulated by developmental, hormonal and environmental signals. We demonstrate previously that the expression of a Melilotus alba expansin gene is up-regulated during the interaction with Sinorhizobium meliloti. Here we describe the effect of phytohormones on expansin gene expression during the development of the nitrogen-fixing symbiosis with rhizobia. Increased accumulation of expansin gene transcripts was observed in roots treated with cytokinin, however neither northern nor RT-PCR analysis appeared to be sensitive enough to detect expansin gene expression in untreated versus treated roots at early time points after treatment with auxin. Additionally, expansin transcripts were found in the nodule cells that are undergoing growth, including the cells of nodule meristem, but not reliable within root hair. As shown for other plant tissues, our results suggest that expansins in legume correlates with proliferation and expansion activities of nodule tissues.