Plants make galls to accommodate foreigners: some are friends, most are foes

New Phytologist, Wiley, 2019, 225 (5), pp.1852-1872

Marion Harris 1, 2, Andrea Pitzschke 3

 
1 IRBI - Institut de recherche sur la biologie de l'insecte UMR7261, Université de Tours, 37000, France
2 Le Studium Loire Valley Institute for Advanced Studies, 45000 Orléans, France
3 Department of Biosciences, Salzburg University, Austria

Abstract

At the colonization site of a foreign entity, plant cells alter their trajectory of growth and development. The resulting structure – a plant gall – accommodates various needs of the foreigner, which are phylogenetically diverse: viruses, bacteria, protozoa, oomycetes, true fungi, parasitic plants, and many types of animals, including rotifers, nematodes, insects, and mites. The plant species that make galls also are diverse. We assume gall production costs the plant. All is well if the foreigner provides a gift that makes up for the cost. Nitrogen‐fixing nodule‐inducing bacteria provide nutritional services. Gall wasps pollinate fig trees. Unfortunately for plants, most galls are made for foes, some of which are deeply studied pathogens and pests: Agrobacterium tumefaciens, Rhodococcus fascians, Xanthomonas citri, Pseudomonas savastanoi, Pantoea agglomerans, ‘Candidatus’ phytoplasma, rust fungi, Ustilago smuts, root knot and cyst nematodes, and gall midges. Galls are an understudied phenomenon in plant developmental biology. We propose gall inception for discovering unifying features of the galls that plants make for friends and foes, talk about molecules that plants and gall‐inducers use to get what they want from each other, raise the question of whether plants colonized by arbuscular mycorrhizal fungi respond in a gall‐like manner, and present a research agenda.

Keywords

Developmental plasticity
Effectors
Morphogenesis
Mutualism
Plant defense
Parasitism
Plant susceptibility
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New Phytologist