The Polyadenylation Factor Subunit CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR30: A Key Factor of Programmed Cell Death and a Regulator of Immunity in Arabidopsis  

Abstract

Programmed cell death (PCD) is essential for several aspects of plant life, including development and stress responses. Indeed, incompatible plant-pathogen interactions are well known to induce the hypersensitive response, a localized cell death. Mutational analyses have identified several key PCD components, and we recently identified the mips1 mutant of Arabidopsis (Arabidopsis thaliana), which is deficient for the key enzyme catalyzing the limiting step of myoinositol synthesis. One of the most striking features of mips1 is the light-dependent formation of lesions on leaves due to salicylic acid (SA)-dependent PCD, revealing roles for myoinositol or inositol derivatives in the regulation of PCD. Here, we identified a regulator of plant PCD by screening for mutants that display transcriptomic profiles opposing that of the mips1 mutant. Our screen identified the oxt6 mutant, which has been described previously as being tolerant to oxidative stress. In the oxt6 mutant, a transfer DNA is inserted in the CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR30 (CPSF30) gene, which encodes a polyadenylation factor subunit homolog. We show that CPSF30 is required for lesion formation in mips1 via SA-dependent signaling, that the prodeath function of CPSF30 is not mediated by changes in the glutathione status, and that CPSF30 activity is required for Pseudomonas syringae resistance. We also show that the oxt6 mutation suppresses cell death in other lesion-mimic mutants, including lesion-simulating disease1, mitogen-activated protein kinase4, constitutive expressor of pathogenesis-related genes5, and catalase2, suggesting that CPSF30 and, thus, the control of messenger RNA 39 end processing, through the regulation of SA production, is a key component of plant immune responses.

Involvement of Arabidopsis Hexokinase1 in Cell Death Mediated byMyo-Inositol Accumulation

“…It confirms our previous work (Bruggeman et al, 2014), showing that although lesion formation was totally abolished in the mips1 oxt6 double mutant, defects in root elongation were still present and that rescue of the cotyledon phenotype was only partial, suggesting that these two developmental pathways are only partly dependent on the spontaneous cell death phenotype. This observation further supports the notion that HXK-dependent regulation of MIPS2 expression according to growth conditions is a key component of MI-dependent PCD regulation.…”

“…We showed that CPSF30 activity was required for lesion formation in mips1 via SA-dependant signaling (Bruggeman et al, 2014). Furthermore, CPSF30 activity was also necessary for PCD establishment in cat2, lesion-simulating disease1, constitutive expressor of pathogenesis-related genes5 (cpr5), and mitogenactivated protein kinase4 Arabidopsis mutants, indicating that posttranscriptional regulation plays a key role in the control of PCD.…”

Chloroplast Activity and 3′phosphadenosine 5′phosphate Signaling Regulate Programmed Cell Death in Arabidopsis

“…In mips1, we did not detect a significant difference between leaves displaying lesions and healthy leaves. Furthermore, even in LD when lesion formation was severe, we did not observe a sharp increase in ROI accumulation, indicating that ROI production occurs only locally, consistent with previously obtained results with 3,39-diaminobenzidine staining (Bruggeman et al, 2014).…”

“…This was the case even in mips1 mips2/+ sesquimutants, in which MI accumulation is further reduced compared with mips1 single mutants. Data reported here do not support a role for oxidative stress in the onset of PCD in mips1, in line with the finding that the cellular redox status is not altered in mips1 under LD conditions (Bruggeman et al, 2014). The latter hypothesis is further confirmed by the observation that EX-dependent 1 O 2 signaling is not involved in triggering cell death in mips1.…”

“…In line with this hypothesis, direct measurement of ROI accumulation in mips1 using EPR spectroscopy did not reveal a global increase in ROI production, even after lesions appeared. We have shown that local ROI production does occur at the site of lesion formation (Bruggeman et al, 2014). However, we have also reported that the mips1 mutant is more tolerant than the wild type to oxidative stress (Meng et al, 2009).…”