Delayed Chlorosis in Arabidopsis Ecotype Dijon-G During Bacterial Infection and Dark-Induced Senescence

Comparative evaluation of defence responses in different Arabidopsis ecotypes to pathogens is useful for understanding how plants acquire disease resistance and finding valuable genetic resources for disease resistance. In this study, leaf chlorosis was delayed in Arabidopsis ecotype Dijon-G (Di-G) in response to Xanthomonas campestris pv. campestris (Xcc) 8004 infection, as well as continuous darkness compared to the ecotype Columbia-0 (Col-0). However, Xcc bacterial proliferation within Di-G was slightly higher in Col-0. The Xcc infection led to lower expression of several pathogenesis-related genes (PDIOX, GLIP1 and PAD4) and senescence-related genes (DIN6 and SAG12) in Di-G. Dark-induced leaf senescence was delayed in detached Di-G leaves, showing a higher chlorophyll content than that of Col-0. Exogenous SA did not change the chlorophyll loss in the Xcc-inoculated Col-0 or Di-G leaves, but SA limited Xcc growth in Col-0 but not in Di-G. SA pretreatment compromised chlorophyll loss in Col-0 during dark-induced leaf senescence, but it remained unaltered in Di-G. These results show that Di-G may have more efficient machinery for attenuating chlorophyll degradation during Xcc bacterial infection and continuous darkness than Col-0. The different sensitivities to exogenous SA in Col-0 and Di-G suggest that the two ecotypes have adapted differently to their natural habitats in terms of plant immunity and leaf senescence.