An attack of plants by pathogens or treatment with certain resistance-inducing compounds can lead to the establishment of a unique primed state of defense. Primed plants show enhanced defense reactions upon further challenge with biotic or abiotic stress. Here, we report that the primed state in Arabidopsis (Arabidopsis thaliana) is still functional in the next generation without additional treatment. We compared the reactions of Arabidopsis plants that had been either primed with b-aminobutyric acid (BABA) or with an avirulent isolate of the bacteria Pseudomonas syringae pv tomato (PstavrRpt2). The descendants of primed plants showed a faster and higher accumulation of transcripts of defense-related genes in the salicylic acid signaling pathway and enhanced disease resistance upon challenge inoculation with a virulent isolate of P. syringae. In addition, the progeny of primed plants was also more resistant against the oomycete pathogen Hyaloperonospora arabidopsidis. When transgenerationally primed plants were subjected to an additional priming treatment, their descendants displayed an even stronger primed phenotype, suggesting that plants can inherit a sensitization for the priming phenomenon. Interestingly, this primed to be primed phenotype was much reduced in the Arabidopsis b-amino-butyric acid priming mutant ibs1 (induced BABA sterility1). Our results demonstrate that the primed state of plants is transferred to their progeny and confers improved protection from pathogen attack as compared to the descendants of unprimed plants.

Hypersensitive response (HR) is a programmed cell death that is commonly associated with disease resistance in plants. Among the different HR-related early induced genes, the AtMYB30 gene is specifically, rapidly, and transiently expressed during incompatible interactions between Arabidopsis and bacterial pathogens. Its expression was also shown to be deregulated in Arabidopsis mutants affected in the control of cell death initiation. Here, we demonstrate that overexpression in Arabidopsis and tobacco of AtMYB30 (i) accelerates and intensifies the appearance of the HR in response to different avirulent bacterial pathogens, (ii) causes HR-like responses to virulent strains, and (iii) increases resistance against different bacterial pathogens, and a virulent biotrophic fungal pathogen, Cercospora nicotianae. In antisense AtMYB30 Arabidopsis lines, HR cell death is strongly decreased or suppressed in response to avirulent bacterial strains, resistance against different bacterial pathogens decreased, and the expression of HR-and defense-related genes was altered. Taken together, these results strongly suggest that AtMYB30 is a positive regulator of hypersensitive cell death.

The circadian clock controls numerous physiological and molecular processes in organisms ranging from fungi to human. In plants, these processes include leaf movement, stomata opening, and expression of a large number of genes. At the core of the circadian clock, the central oscillator consists of a negative autoregulatory feedback loop that is coordinated with the daily environmental changes, and that generates the circadian rhythms of the overt processes. Phosphorylation of some of the central oscillator proteins is necessary for the generation of normal circadian rhythms of Drosophila , humans, and Neurospora , where CK1 and CK2 are emerging as the main protein kinases involved in the phosphorylation of PER and FRQ. We have previously shown that in Arabidopsis , the protein kinase CK2 can phosphorylate the clock-associated protein CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) in vitro . The overexpression of one of its regulatory subunits, CKB3, affects the regulation of circadian rhythms. Whether the effects of CK2 on the clock were due to its phosphorylation of a clock component had yet to be proven. By examining the effects of constitutively expressing a mutant form of the Arabidopsis clock protein CCA1 that cannot be phosphorylated by CK2, we demonstrate here that CCA1 phosphorylation by CK2 is important for the normal functioning of the central oscillator.

We hereby confirm that the original images are those first published in PNAS. When preparing the figures for submission to PNAS, the raw images were cropped and/or stretched to match the other blots and saved in the format for submission. Unfortunately, we did not systematically archive an independent copy of each raw image, and only the final version of the figures was stored. Fig. 3 appears to have areas of unmarked splicing and background inconsistencies, but we are confident, however, in the scientific accuracy of the data despite being unable to provide the original images."Further, we acknowledge that images of yeast colonies in Fig. S1B are indeed duplicated. Our intention was to represent the presence (or absence) of yeast growth observed with the different protein combinations. We recognize that this should have been clearly indicated in the figure legend and apologize for this omission. We have been able to retrieve the original results and prepared the revised figure below showing growth of yeast colonies expressing the different protein combinations. We apologize for any inconvenience the publication of these figures may have caused." The corrected Fig. S1 and its corrected legend appear below. The SI has been corrected online.