Receptor-like cytoplasmic kinases of different subfamilies differentially regulate SOBIR1/BAK1-mediated immune responses in Nicotiana benthamiana.

Cell-surface receptors form the front line of plant immunity. The leucine-rich repeat (LRR)-receptor-like kinases SOBIR1 and BAK1 are required for the functionality of the tomato LRR-receptor-like protein Cf-4, which detects the secreted effector Avr4 of the pathogenic fungus Fulvia fulva. Here, we show that the kinase domains of SOBIR1 and BAK1 directly phosphorylate each other and that residues Thr522 and Tyr469 of the kinase domain of Nicotiana benthamiana SOBIR1 are required for its kinase activity and for interacting with signalling partners, respectively. By knocking out multiple genes belonging to different receptor-like cytoplasmic kinase (RLCK)-VII subfamilies in N. benthamiana:Cf-4, we show that members of RLCK-VII-6, -7, and -8 differentially regulate the Avr4/Cf-4-triggered biphasic burst of reactive oxygen species. In addition, members of RLCK-VII-7 play an essential role in resistance against the oomycete pathogen Phytophthora palmivora. Our study provides molecular evidence for the specific roles of RLCKs downstream of SOBIR1/BAK1-containing immune complexes.

Genotypic richness and phenotypic dissimilarity enhance population performance.

Increases in biodiversity can result from an increase in species richness, as well as from a higher genetic diversity within species. Intraspecific genetic diversity, measured as the number of genotypes, can enhance plant primary productivity and have cascading effects at higher trophic levels, such as an increase in herbivore and predator richness. The positive effects of genotypic mixtures are not only determined by additive effects, but also by interactions among genotypes, such as facilitation or inhibition. However, so far there has been no effort to predict the extent of such effects. In this study, we address the question of whether the magnitude of the effect of genotype number on population performance can be explained by the extent of dissimilarity in key traits among genotypes in a mixture. We examine the relative contribution of genotype number and phenotypic dissimilarity among genotypes to population performance of the soil arthropod, Orchesella cincta. Nearly homogeneous genotypes were created from inbred isofemale lines. Phenotypic dissimilarity among genotypes was assessed in terms of three life-history traits that are associated with population growth rate, i.e., egg size, egg development time, and juvenile growth rate. A microcosm experiment with genotype mixtures consisting of one, two, four, and eight genotypes, showed that genotypic richness strongly increased population size and biomass production and was associated with greater net diversity effects. Most importantly, there was a positive log-linear relationship between phenotypic dissimilarity in a mixture and the net diversity effects for juvenile population size and total biomass. In other words, the degree of phenotypic dissimilarity among genotypes determined the magnitude of the genotypic richness effect, although this relationship leveled off at higher values of phenotypic dissimilarity. Although the exact mechanisms responsible for these effects are currently unknown, similar advantages of trait dissimilarity have been found among species. Hence, to better understand population performance, genotype number and phenotypic dissimilarity should be considered collectively.