Clarke, C. R. | Search bioRxiv

bioRxiv2022

Steroidal glycoalkaloids contribute to anthracnose resistance in Solanum lycopersicum

Anthracnose is a widespread plant disease caused by various species of the fungal pathogen Colletotrichum. In solanaceous plants such as tomato (Solanum lycoperiscum), Colletotrichum infections exhibit a quiescent, asymptomatic state in developing fruit, followed by a transition to necrotrophic infections in ripe fruit. Through analysis of fruit tissue extracts of 95L368, a tomato breeding line that yields fruit with enhanced anthracnose resistance, we identified a role for steroidal glycoalkaloids (SGAs) in anthracnose resistance. The SGA -tomatine and several of its derivatives accumulated at higher levels, in comparison to fruit of the susceptible tomato cultivar US28, 95L368 fruit extracts with fungistatic activity against Colletotrichum. Correspondingly, ripe and unripe 95L368 fruit displayed enhanced expression of glycoalkaloid metabolic enzyme (GAME) genes, which encode key enzymes in SGA biosynthesis. Metabolomics analysis incorporating recombinant inbred lines (RILs) generated from 95L368 and US28 yielded strong positive correlations between anthracnose resistance and accumulation of -tomatine and several derivatives. Lastly, transient silencing of expression of the GAME genes GAME31 and GAME5 in anthracnose-susceptible tomato fruit yielded enhancements to anthracnose resistance. Together, our data support a role for SGAs in anthracnose defense in tomato, with a distinct SGA metabolomic profile conferring resistance to virulent Colletotrichum infections in ripe fruit. HighlightThis work describes an important role for steroidal glycoalkaloids (SGAs), abundant secondary metabolites in tomato fruit, in defense against anthracnose, a widespread fungal disease that impacts diverse crop species.

plant biology↗

bioRxiv2021

Experimental evidence pointing to rain as a reservoir of tomato phyllosphere microbiota

Plant microbiota play essential roles in plant health and crop productivity. Comparisons of community composition have suggested seeds, soil, and the atmosphere as reservoirs of phyllosphere microbiota. After finding that leaves of tomato (Solanum lycopersicum) plants exposed to rain carried a higher microbial population size than leaves of tomato plants not exposed to rain, we experimentally tested the hypothesis that rain is a so far neglected reservoir of phyllosphere microbiota. Rain microbiota were thus compared with phyllosphere microbiota of tomato plants either treated with concentrated rain microbiota, filter-sterilized rain, or sterile water. Based on 16S rRNA amplicon sequencing, one-hundred and four operational taxonomic units (OTUs) significantly increased in relative abundance after inoculation with concentrated rain microbiota but no OTU significantly increased after treatment with either sterile water or filter-sterilized rain. Some of the genera to which these 104 OTUs belonged were also found at higher relative abundance on tomatoes exposed to rain outdoors than on tomatoes grown protected from rain in a commercial greenhouse. Taken together, these results point to precipitation as a reservoir of phyllosphere microbiota and show the potential of controlled experiments to investigate the role of different reservoirs in the assembly of phyllosphere microbiota.

microbiology↗