Poster: Plant-symbiont interactions

Abs # 592: A bean Nod- mutant is impaired in primary symbiotic events.

Presenter:	Quinto, Carmen , quinto@ibt.unam.mx
Authors	Quinto, Carmen  (A)   Cardenas, Luis  (A)   Aleman, Emilia  (A)   Nava, Noreide  (A)   Santana, Olivia  (A)
Affiliations:	(A): Institute of Biotechnology, Cuernavaca, Mor. Mexico A. P. 510-3, C.P. 62251
Web Site:	http://WWW.IBT.UNAM.MX

Legumes are unique in their capability to establish a symbiotic relationship with soil bacteria of the Rhizobiaceae family. First, flavonoids excreted by the host plant roots switch on the nodulation genes in the microsymbionts. Then, the Nod factors (NFs) are produced and perceived in a specific manner by the host plants. NFs induce cellular and molecular responses such as ion fluxes and depolarization of the plasma membrane, calcium changes, phosphatidic acid and diacylglycerol formation, accumulation of reactive oxygen species, root hair deformation involving changes in the actin cytoskeleton, and early nodulin gene expression. Some of the responses are induced in the plant at very low NF concentratrions (10-12 M), suggesting that they are recognized by high affinity receptors. Although the overall signaling events between both simbionts are well understood, further steps involving signal recognition and transduction by the host plant are yet to be fully determined. Plant mutations affecting nodulation have facilitated the understanding of this process. Recently, using this approach, two LysM/type serine/threonine receptor kinases genes, NFR1 and NFR5 have been reported that enable the model legume Lotus japonicus to recognize its bacterial microsymbiont Mezorhizobium loti (Radutoi et al., 2003). Here, we describe the characterization of a P. vulgaris DOR364 non-nodulating mutant by molecular and cell biology criteria. Root hair cells of the non-nodulating plant, respond with swelling and branching when inoculated with Rhizobium etli, albeit not with curling. Additionally, neither initiation of cell divisions in the outer cortex, nor entrapment of bacteria or infection thread formation were observed. Both, the bean DOR364 wild-type and the mutant responded with elevated root hair intracellular calcium changes. The expression pattern of the early nodulin, ENOD40, in the non-nodulating mutant diverged as compared to the wild type parental plant. Furthermore, this Nod- bean mutant is able to form a normal arbuscular mycorrhiza interaction when inoculated with Glomus intraradices, after five weeks of inoculation. With all these data, we propose that the non-nodulating DOR 364 bean mutant is not blocked in Nod factor perception by receptors previously described, but later in some of the early steps involved in the signal transduction pathway. Supported by grants IN209202, DGAPA/UNAM and 33056-N, CONACyT.