Fungal phytopathogens encode functional homologues of plant rapid alkalinization factor (RALF) peptides.
In this article, we describe the presence of genes encoding close homologues of an endogenous plant peptide, rapid alkalinization factor (RALF), within the genomes of 26 species of phytopathogenic fungi. Members of the RALF family are key growth factors in plants, and the sequence of the RALF active region is well conserved between plant and fungal proteins. RALF1-like sequences were observed in most cases; however, RALF27-like sequences were present in the Sphaerulina musiva and Septoria populicola genomes. These two species are pathogens of poplar and, interestingly, the closest relative to their respective RALF genes is a poplar RALF27-like sequence. RALF peptides control cellular expansion during plant development, but were originally defined on the basis of their ability to induce rapid alkalinization in tobacco cell cultures. To test whether the fungal RALF peptides were biologically active in plants, we synthesized RALF peptides corresponding to those encoded by two sequenced genomes of the tomato pathogen Fusarium oxysporum f. sp. lycopersici. One of these peptides inhibited the growth of tomato seedlings and elicited responses in tomato and Nicotiana benthamiana typical of endogenous plant RALF peptides (reactive oxygen species burst, induced alkalinization and mitogen-activated protein kinase activation). Gene expression analysis confirmed that a RALF-encoding gene in F. oxysporum f. sp. lycopersici was expressed during infection on tomato. However, a subsequent reverse genetics approach revealed that the RALF peptide was not required by F. oxysporum f. sp. lycopersici for infection on tomato roots. This study has demonstrated the presence of functionally active RALF peptides encoded within phytopathogens that harbour an as yet undetermined role in plant-pathogen interactions.
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Elisha
E
Thynne
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Isabel M L
IML
Saur
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Jaime
J
Simbaqueba
Evolution, Ecology and Genetics Division, Research School of Biology, The Australian National University, Canberra, 2601, Australia.|Computational Evolution Group, The University of Auckland, Auckland, 1142, New Zealand.
Huw A
HA
Ogilvie
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Yvonne
Y
Gonzalez-Cendales
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Oliver
O
Mead
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Adam
A
Taranto
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Ann-Maree
AM
Catanzariti
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Megan C
MC
McDonald
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Benjamin
B
Schwessinger
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
David A
DA
Jones
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
John P
JP
Rathjen
Plant Sciences Division, The Australian National University, Canberra, 2601, Australia.
Peter S
PS
Solomon
D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005670:Fusarium / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D036361:Peptide Hormones / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D036226:Seedlings / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism / Q000382:microbiology
D005656:Fungal Proteins; D036361:Peptide Hormones; D010940:Plant Proteins
Fusarium; phytopathogen effectors; rapid alkalinization factor (RALF)