Abstract
Plant-parasitic root-knot nematodes induce the formation of giant cells within the plant root, and it has been recognized that auxin accumulates in these feeding sites. Here, we studied the role of the auxin transport system governed by AUX1/LAX3 influx proteins and different PIN efflux proteins during feeding site development in Arabidopsis thaliana roots. Data generated via promoter-reporter line and protein localization analyses evoke a model in which auxin is being imported at the basipetal side of the feeding site by the concerted action of the influx proteins AUX1 and LAX3, and the efflux protein PIN3. Mutants in auxin influx proteins AUX1 and LAX3 bear significantly fewer and smaller galls, revealing that auxin import into the feeding sites is needed for their development and expansion. The feeding site development in auxin export (PIN) mutants was only slightly hampered. Expression of some PINs appears to be suppressed in galls, probably to prevent auxin drainage. Nevertheless, a functional PIN4 gene seems to be a prerequisite for proper nematode development and gall expansion, most likely by removing excessive auxin to stabilize the hormone level in the feeding site. Our data also indicate a role of local auxin peaks in nematode attraction towards the root.
Highlights
Plant roots are constantly challenged by pathogens and parasites present in the rhizosphere
Because our observations strongly suggest that auxin transport plays different roles during those two phases, our results will here be discussed per infection phase
Our results show that pin4 mutants, reported to accumulate higher auxin levels in the root tip (Friml et al, 2002a), are more susceptible to root-knot nematodes (RKN) penetration, as seen by the high number of juveniles within the plant host (3–7 days after inoculation (DAI))
Summary
Plant roots are constantly challenged by pathogens and parasites present in the rhizosphere. Plant-parasitic nematodes (PPN) inflict considerable damage to a wide range of plant species (Sasser and Freckman, 1986). Because of their economic importance, the best-studied nematodes are the cyst nematodes (CN; Heterodera and Globodera spp.) and root-knot nematodes (RKN; Meloidogyne spp.), which are both biotrophs with sedentary lifestyles. GC formation starts with the induction of binucleate cells (de Almeida Engler et al, 1999, 2011) followed by repeated rounds of nuclear division, DNA amplification, and cell growth in the absence of cytokinesis This process, which occurs in five to seven cells around the nematode head, causes them
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