Physiological effects of major up-regulated Alnus glutinosa peptides on Frankia sp. ACN14a

Abstract

Alnus glutinosa has been shown previously to synthesize, in response to nodulation by Frankia sp. ACN14a, an array of peptides called Alnus symbiotic up-regulated peptides (ASUPs). In a previous study one peptide (Ag5) was shown to bind to Frankia nitrogen-fixing vesicles and to modify their porosity. Here we analyse four other ASUPs, alongside Ag5, to determine whether they have different physiological effects on in vitro grown Frankia sp. ACN14a. The five studied peptides were shown to have different effects on nitrogen fixation, respiration, growth, the release of ions and amino acids, as well as on cell clumping and cell lysis. The mRNA abundance for all five peptides was quantified in symbiotic nodules and one (Ag11) was found to be more abundant in the meristem part of the nodule. These findings point to some peptides having complementary effects on Frankia cells.

The PEG-responding desiccome of the alder microsymbiont Frankia alni

“…F. alni strain ACN14a 69 was grown in liquid BAP- medium without ammonium as described earlier 70 . The cells were then syringed thoroughly with needles of decreasing width (21G–27G), the cells OD 600 measured and the suspension diluted prior to inoculation.…”

The mycorrhiza-dependent defensin MtDefMd1 of Medicago truncatula acts during the late restructuring stages of arbuscule-containing cells

“…Interestingly, nodule-specific defensins were found in Alnus glutinosa root nodules [ 69 ]. AG5, one of these, caused physiological changes of Frankia vesicles and increased their permeability [ 69 ], whereas four additional defensins displayed partly overlapping functions [ 70 ]. Apart from classical non-symbiotic and symbiotic defensins, more than 700 defensin-like peptides containing N-terminal signal peptides and conserved cysteine residues were identified in legume plants [ 26 ].…”

The non-specific Lipid Transfer Protein (nsLTP) is involved at early and late stages of symbiosis between Alnus glutinosa and Frankia alni

“…Metabolomics on an Alnus-infective strain showed the presence of various compounds absent from roots (12), high levels of TCA intermediates citrate, fumarate and malate (13) and high levels of citrulline, glutamate and pyruvate (14,15).. Signalling between alder and Frankia alni involves on the part of the bacterium the synthesis of an uncharacterized root hair deforming factor (16,17) and that of the auxin PAA (18). On the plant side, less is known besides the upregulation of defensins that modify the porosity of Frankia membranes (19,20).…”

“…Signalling between alder and Frankia alni involves on the part of the bacterium the synthesis of an uncharacterized root hair deforming factor (Ghelue et al ., 1997; Cérémonie et al ., 1999) and that of the auxin PAA (Hammad et al ., 2003). On the plant side, less is known besides the upregulation of defensins that modify the porosity of Frankia membranes (Carro et al ., 2015b; Carro et al ., 2016).…”