Enhanced Salicylic Acid Biosynthesis Is Involved in Heterosis for Bacterial Defense in Arabidopsis

We provide evidence that heterosis for bacterial defense exists in hybrids crossed between some Arabidopsis accessions. Comparison of transcriptomes between hybrids exhibiting heterosis for disease resistance and their parents after inoculation with Pst DC3000 revealed that several key genes involved in salicylic acid (SA) biosynthesis were significantly up-regulated in hybrids. Consistently, in response to bacterial infection, more SA [both free SA and SA glycoside (SAG)] accumulated in hybrids compared with both parents. In addition, heterosis for bacterial defense was significantly compromised in hybrids of pad4 mutants in which the SA biosynthesis pathway was blocked. Moreover, we further revealed that increased histone H3 acetylation of the key genes involved in the SA biosynthesis pathway correlated with their up-regulated expression in hybrids. Around 30 inoculated leaves from Arabidopsis accessions Col-0 and Sei-0 as well as their reciprocal hybrids Fcs and Fsc, which showed best-parent heterosis for bacterial defense were pooled in each sample for mRNA Seq using HiSeq 2000 sequencing system (Illumina)