Transport of Amino Acid and Sugar Regulated by MAMPs Triggered Immunity in Arabidopsis thaliana

Microbe Associated Molecular Pattern (MAMP)-triggered Immunity (MTI) effectively helps plants suppress infections by bacterial pathogens, but the underlying mechanisms are not fully understood. Transcriptional analysis of MTI in plants showed that amino acid (AA) and sugar transporter genes are responsive to MAMPs. To determine whether MTI modifies AAs and sugar transport and understand which transporter genes are involved in this process, I used radioactively labeled substrates and kinetic assays to approach this question in the model plant Arabidopsis thaliana. I found that AA transport in Arabidopsis seedlings was suppressed by MTI in the first hour post-elicitation and then enhanced by MTI until 24 hours. LHT1(Lysine Histidine Transporter 1), a broad AA transporter, was necessary for the enhanced transport of AA in MTI. Moreover, I found that AAs accumulated in both seedlings and the leaves of adult plants when MTI was triggered. This enhanced transport and accumulation of AAs depended partially on the plant hormone salicylic acid (SA). Glutamine (Gln) and serine (Ser) were among the AAs that accumulated in plants, suppressed virulence and growth of the bacterial pathogen Pseudomonas syringae, and therefore may be part of a potential mechanism by which MTI inhibits bacterial virulence and growth. On the other hand, long-distance transport (translocation)of sucrose from leaf to sink tissue was slowed down by MTI through the action of the sucrose transporter gene SUC1(Sucrose Proton symporter 1). The suc1 mutant did not modify the translocation of sucrose in MTI and showed susceptibility to a non-pathogenic bacterial pathogen, which suggests a compromised MTI response. In addition, glucose transport in seedlings was enhanced by MTI as early as 8 hours after elicitation. SA also regulated the transport of glucose but not the translocation of sucrose. Loss of sugar transporter genes SWEET1 and SWEET17 led to hexose accumulation and susceptibility to Pseudomonas syringae. Moreover, the sweet1 mutant had an altered level of secondary metabolites produced in MTI. These studies demonstrate that plants orchestrate AA and sugar transport as well as the concentration of these primary metabolites in MTI to defend against Pseudomonas syringae, providing new molecular mechanisms of MTI suppressing microbe infection and how SA promotes MTI responses. These findings will shed light on crop yield improvement in agriculture.