Identification of a wheat polygalacturonase-inhibiting protein involved in Fusarium head blight resistance

The plant cell wall is the first barrier to obstruct attack by pathogens. The polygalacturonase-inhibiting protein (PGIP) can specifically recognize and inhibit polygalacturonase (PG), a hydrolase that is secreted by fungi to invade plants, thus protecting plants from fungal infection by reducing the hydrolytic activity of PGs. In this study, we cloned a novel PGIP gene, Tapgip3, that is located on the 7D chromosome and encoded a 791 amino acid protein in the Fusarium head blight (FHB)-resistant wheat cultivar Ning7840. The real-time PCR analysis showed that this gene was upregulated sharply in spikes at 48 h after infection by either Fusarium graminearum or the trichothecene deoxynivalenol (DON). Subcellular localization analysis revealed that TaPGIP3 was secreted on the plant cell wall. When the transcripts of Tapgip3 were knocked down by barley stripe mosaic virus-virus-induced gene silencing (BSMV-VIGS), the growth of F. graminearum hyphae was promoted with larger lesions on wheat leaves. This suggests that Tapgip3 plays an important role in the response to F. graminearum infection. Although salicylic acid (SA), methyl jasmonate (MeJA) and abscisic acid (ABA) have been reported to be involved in wheat FHB resistance, we demonstrate in our study that the two copies of Tapgip3 are negatively regulated by these three hormones and positively regulated by indoleacetic acid (IAA).