The MtMMPL1 Early Nodulin Is a Novel Member of the Matrix Metalloendoproteinase Family with a Role in Medicago truncatula Infection by Sinorhizobium meliloti  

Abstract

We show here that MtMMPL1, a Medicago truncatula nodulin gene previously identified by transcriptomics, represents a novel and specific marker for root and nodule infection by Sinorhizobium meliloti. This was established by determining the spatial pattern of MtMMPL1 expression and evaluating gene activation in the context of various plant and bacterial symbiotic mutant interactions. The MtMMPL1 protein is the first nodulin shown to belong to the large matrix metalloendoproteinase (MMP) family. While plant MMPs are poorly documented, they are well characterized in animals as playing a key role in a number of normal and pathological processes involving the remodeling of the extracellular matrix. MtMMPL1 represents a novel MMP variant, with a substitution of a key amino acid residue within the predicted active site, found exclusively in expressed sequence tags corresponding to legume MMP homologs. An RNA interference approach revealed that decreasing MtMMPL1 expression leads to an accumulation of rhizobia within infection threads, whose diameter is often significantly enlarged. Conversely, MtMMPL1 ectopic overexpression under the control of a constitutive (35S) promoter led to numerous abortive infections and an overall decrease in the number of nodules. We discuss possible roles of MtMMPL1 during Rhizobium infection.

EFD Is an ERF Transcription Factor Involved in the Control of Nodule Number and Differentiation inMedicago truncatula

“…Importantly, in situ hybridizations showed that Mt RR4 and more generally the type-A response regulator gene family are expressed in nodule zone II, consistent with the EFD expression pattern (see Supplemental Figure 9 online). Other nodulin genes expressed in nodule zone II, such as Mt N6 (Mathis et al, 1999), Mt ENOD11 , and Mt MMPL1 (Combier et al, 2007), were not found to be similarly affected in the efd-1 and P35S:EFD:VP16 samples (see Supplemental Table 5 online).…”

“…As a negative control, to detect any possible nonspecific trans-activation effect, we used a Mt MMPL1 promoter:GUS fusion not controlled by EFD (previous array analyses) and showing a very low basal level of expression in these tissues (Combier et al, 2007). Quantitative analyses of GUS activity in N. benthamiana leaf extracts revealed that the Mt RR4 promoter was clearly activated (on average 8.5-fold on three biological repetitions) by either EFD:RFP ( Figures 9A and 9B) or EFD:HA fusions (see Supplemental Figure 11 online).…”

“…Plants in pouches were inoculated with 600 mL of Sinorhizobium meliloti suspension at an OD 600 = 0.02 and placed at 258C (light-dark photoperiod: 16 h/8 h). Plant growth and inoculation in caisson were as described by Combier et al (2007), with the following chamber conditions: temperature, 228C; 75% hygrometry; light intensity, 200 mE·m 22 ·s 21 ; light-dark photoperiod, 16 h/ 8 h. For ACC and AVG treatments, plants were grown on Farhaeus medium in plates at 208C with the same photoperiod.…”

Differential response of the plant Medicago truncatula to its symbiont Sinorhizobium meliloti or an exopolysaccharide-deficient mutant

“…A small number of genes have been previously determined, by Northern blot analysis or real-time PCR, to be differentially expressed between wild-typeand exo mutant-inoculated roots (34)(35)(36)(37). Our data set, which represents roots harvested at 3 dpi, is earlier than the time points at which expression was assayed for most of the genes previously determined to be differentially expressed (34)(35)(36).…”

NMMP1, a Matrix Metalloprotease in Nicotiana benthamiana Has a Role in Protection against Bacterial Infection

“…Several matrixins have been isolated from plants, including soybean (Graham et al, 1991;Liu et al, 2001;McGeehan et al, 1992;Pak et al, 1997), Arabidopsis (Maidment et al, 1999;Golldack et al, 2002), cucumber (Delorme et al, 2000), alfalfa (Combier et al, 2007), Pinus taeda (Ratnaparkhe et al, 2009), and Nicotiana tabacum (Schiermeyer, 2009). Matrixins have zinc at their catalytic center and are sensitive to EDTA (McGeehan et al, 1992).…”