Parasitic Nematodes Modulate PIN-Mediated Auxin Transport to Facilitate Infection

Plant-parasitic nematodes are destructive plant pathogens that cause significant yield losses. They induce highly specialized feeding sites (NFS) in infected plant roots from which they withdraw nutrients. In order to establish these NFS, it is thought that the nematodes manipulate the molecular and physiological pathways of their hosts. Evidence is accumulating that the plant signalling molecule auxin is involved in the initiation and development of the feeding sites of sedentary plant-parasitic nematodes. Intercellular transport of auxin is essential for various aspects of plant growth and development. Here, we analysed the spatial and temporal expression of PIN auxin transporters during the early events of NFS establishment using promoter-GUS/GFP fusion lines. Additionally, single and double pin mutants were used in infection studies to analyse the role of the different PIN proteins during cyst nematode infection. Based on our results, we postulate a model in which PIN1-mediated auxin transport is needed to deliver auxin to the initial syncytial cell, whereas PIN3 and PIN4 distribute the accumulated auxin laterally and are involved in the radial expansion of the NFS. Our data demonstrate that cyst nematodes are able to hijack the auxin distribution network in order to facilitate the infection process

Expression of the Arabidopsis jasmonate signalling repressor JAZ1/TIFY10A is stimulated by auxin

Plant hormones have pivotal roles in almost every aspect of plant development. Over the past decades, physiological and genetic studies have revealed that hormone action in plants is determined by complex interactions between hormonal signalling pathways. Evidence is accumulating for the existence of crosstalk between the auxin and jasmonate (JA) signalling pathways. Recently, the JASMONATE ZIM-domain (JAZ) proteins have been identified as the long-sought repressors of JA signalling. Here, we show that expression of JAZ1/TIFY10A is not solely inducible by JA, but that it is also an early auxin-responsive gene. Furthermore, we could show that the auxin-inducible expression of JAZ1/TIFY10A is independent of the JA signalling pathway but is controlled by the auxin/indole-3-acetic acid-auxin response transcription factor signalling pathway. Our results provide evidence for the existence of at least two different input signals regarding JAZ1/TIFY10A expression and thus support the idea of an intimate molecular interplay between auxin and JA signalling

Regulatory sequences of Arabidopsis drive reporter gene expression in nematode feeding structures.

In the quest for plant regulatory sequences capable of driving nematode-triggered effector gene expression in feeding structures, we show that promoter tagging is a valuable tool. A large collection of transgenic Arabidopsis plants was generated. They were transformed with a beta-glucuronidase gene functioning as a promoter tag. Three T-DNA constructs, pGV1047, p delta gusBin19, and pMOG553, were used. Early responses to nematode invasion were of primary interest. Six lines exhibiting beta-glucuronidase activity in syncytia induced by the beet cyst nematode were studied. Reporter gene activation was also identified in galls induced by root knot and ectoparasitic nematodes. Time-course studies revealed that all six tags were differentially activated during the development of the feeding structure. T-DNA-flanking regions responsible for the observed responses after nematode infection were isolated and characterized for promoter activity