Arabidopsis exhibits differential response in basal immunity and proline metabolism during defense against host and nonhost pathogen infection

Abstract

A host-pathogen surpasses the plant defense machinery and successfully infects the plant to serve its needs. In contrast, a nonhost pathogen is restricted by plant immune responses. In this study, we deciphered the differential responses of Arabidopsis against the host-pathogen (Pseudomonas syringae pv. maculicola, Psm) and the nonhost pathogen (P. syringae pv. tabaci, Pst) infection. The Pst multiplication was restricted in Arabidopsis plant coinciding with the absence of any disease symptoms which was also associated with the increase in defense associated, pathogenesis related gene1 (PR1) expression and callose deposition. Host-pathogen infection, on the other hand, caused chlorotic symptoms with much less activation of the defense marker genes compared to the nonhost infection. Proline content was decreased in plants infected with Psm but not in case of Pst infection. Proline is a crucial plant metabolite, and osmolyte suggested to be involved in plant defense responses. However, the differential regulation of proline pathway under a susceptible or resistance response has not yet been unravelled. The expression profile of proline metabolism genes in a time course post-infection revealed drastic differences after Psm and Pst pathogen infection. The elevated expression of proline catabolic genes, AtProDH and AtP5CDH were noted under Psm infection. In contrast, plants infected with Pst showed upregulation of AtProDH but a decline in AtP5CDH transcripts along with an upregulation of the biosynthesis genes i.e. AtP5CS and AtP5CR. Our study shows that proline metabolism is tightly regulated under host and nonhost pathogen infection and impacts susceptibility and resistance of the plants, respectively.