Publication Date:
1998-08-04
Description:
Polygalacturonase (PG) is one of the most important enzymes associated with plant cell wall degradation. It has been proposed to participate in the early steps of theRhizobium–legume interaction. We have identified two classes of cDNA fragments corresponding to two classes of PG genes in theMedicagogenome. One of this class, represented by E2inM. truncatulaand Pl1inM. sativa, seems to be related to previously characterized plant PG genes expressed in pollen. We have isolated the genomic clone containing the entire gene corresponding to the second class (E3). We showed thatMsPG3is a single gene in theMedicagogenome coding for PG. By reverse transcription-PCR,MsPG3expression was detected in roots 1 day afterRhizobiuminoculation. The early induction of theMsPG3, as also seen byin situhybridization experiments, supports its involvement in the early stages of theRhizobium-legume infection process. In addition, by analyzing the expression of aMsPG3promoter-gusconstruct inVicia hirsuta-transgenic root nodules, we showed thatMsPG3was expressed in all cells of nodule primordia and in the cells of the invasion zone. By Northern blot,MsPG3transcripts are not detected in variousMedicagotissues, indicating that the function of this gene is related closely to symbiosis. Thus, our results strongly suggest the involvement ofMsPG3gene during meristem formation and/or in the infection process, probably by facilitating cell wall rearrangement, penetration of the bacteria through the root hair wall, or infection thread formation and release of bacteria in plant cells.MsPG3represents a class of PG genes, distinct from the pollen-specific genes, and it is the first pectic encoded enzyme demonstrated to be involved inRhizobium-legume symbiosis.
Print ISSN:
0027-8424
Electronic ISSN:
1091-6490
Topics:
Biology
,
Medicine
,
Natural Sciences in General
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