Characterization of Medicago truncatula mutants defective in infection persistence and defense response during Rhizobium-legume symbiosis
Abstract
Plant mutants with defects in their symbiotic phenotypes can be used as tools to unravel and understand plant functions. To understand the symbiotic process and the role of plant defense responses in regulation of rhizobial infection and modulation, two classes of modulation mutants have been selected. The first class of mutants is characterized by an infection arrest phenotype with no successful infections. This class is represented by pdl, for its poodle root phenotype and lin for lumpy Infections. Neither mutants are capable of nitrogen fixation but both show cortical cell activation in response to Rhizobium. All arrested infections in wild type, lin and pdl are associated with callose deposition in their infection thread walls. Inappropriate induction of host defense responses, as evidenced by callose accumulation, early in the symbiosis might be the indicative of an active infection arrest. Alternatively these mutants might have altered responses to hormones, but under this study the growth responses of root to exogenous hormones were not perturbed. Furthermore, although reduction of ethylene levels using the ethylene biosynthesis inhibitor aminoethoxy-vinylglycine (AVG) was able to rescue the root phenotype of pdl and resulted in some cortical cell proliferation at infection sites, AVG treatment was not able to rescue the arrested infections of pdl. This indicates that the primary genetic defect may not be directly related to ethylene synthesis or perception. The second class of mutants has persistent infections but is accompanied by tissue browning; spk for speckle and bnb for bonbon represent this class. In spk and bnb mutants elicitation of the necrotic response is associated with diminished nodule number or late failure of symbiotic development, respectively. Interestingly, both spk and bnb exhibit increased levels of certain isoflavonoid compounds. These plant mutants may provide a means to elucidate the cellular, molecular and physiological mechanism that govern infection persistence during symbiosis and to determine whether such a process is regulated by plant defense mechanisms.
Description
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Includes bibliographical references: P. 76-85.
Issued also on microfiche from Lange Micrographics.
Includes bibliographical references: P. 76-85.
Issued also on microfiche from Lange Micrographics.
Keywords
biology., Major biology.