Regulatory Factors of Leaf Senescence are Affected in Arabidopsis Plants Overexpressing the Histone Methyltransferase SUVH2

Leaf senescence involves extensive reprogramming of gene expression effectuating the complex biochemical and structural changes that occur during the last stage of leaf development. In a large-scale transcriptomic approach in Arabidopsis thaliana (L.) Heynh., using qRT-PCR, gene expression for more than 380 transcriptional regulators was shown to be regulated in a senescence-specific manner. Overexpression of SUVH2 histone methyltransferase, which was previously reported by Ay and others (Plant J 58:333-346, 2009) to delay leaf senescence, affected gene expression of about 50 % of these senescence-related regulatory factors (SRRFs), whereas the other half was regulated during senescence similar to wild type. Thereby, the senescence-related transcription factor families AP2-EREBP, C2H2, NAC, and WRKY are affected most notably. This suggests a direct or indirect locus-specific mode of SUVH2 action. Interestingly, we found that 45 of the identified SRRFs possess an ERF-associated amphiphilic repression motif, indicating that EAR motif-mediated transcriptional repression could be a principal mechanism within regulation of senescence. Furthermore, about 30 % of the SRRFs are predicted as putative targets of the ELONGATED HYPOCOTYL5 (HY5) bZIP transcription factor. This suggests that HY5-dependent processes play an important role within the regulatory network of leaf senescence. Moreover, these processes seem to be specifically affected in plants overexpressing SUVH2. Our results give new insights into the complex regulatory network of senescence-associated processes and the specific involvement of chromatin alterations.