Abstract
Alternaria brassicicola causes black spot disease of Brassica species. The functional importance of pectin digestion enzymes and unidentified phytotoxins in fungal pathogenesis has been suspected but not verified in A. brassicicola. The fungal transcription factor AbPf2 is essential for pathogenicity and induces 106 genes during early pathogenesis, including the pectate lyase-coding gene, PL1332. The aim of this study was to test the importance and roles of PL1332 in pathogenesis. We generated deletion strains of the PL1332 gene, produced heterologous PL1332 proteins, and evaluated their association with virulence. Deletion strains of the PL1332 gene were approximately 30% less virulent than wild-type A. brassicicola, without showing differences in colony expansion on solid media and mycelial growth in nutrient-rich liquid media or minimal media with pectins as a major carbon source. Heterologous PL1332 expressed as fusion proteins digested polygalacturons in vitro. When the fusion proteins were injected into the apoplast between leaf veins of host plants the tissues turned dark brown and soft, resembling necrotic leaf tissue. The PL1332 gene was the first example identified as a general toxin-coding gene and virulence factor among the 106 genes regulated by the transcription factor, AbPf2. It was also the first gene to have its functions investigated among the 19 pectate lyase genes and several hundred putative cell-wall degrading enzymes in A. brassicicola. These results further support the importance of the AbPf2 gene as a key pathogenesis regulator and possible target for agrochemical development.
Highlights
Alternaria brassicicola is a destructive plant pathogen and causes black spot disease on almost all plant species in the Brassicaceae [1,2,3]
The results of this study provide another reason to further investigate the functions of other genes regulated by AbPf2 and to consider this transcription factor a good target for efficient management of diseases caused by A. brassicicola
Genes encoding pectinolytic enzymes are important virulence factors and their deletion or disruption causes a reduction in virulence of several phytopathogenic fungi, such as Aspergillus flavus, Botrytis cinerea, and Claviceps purpurea [40,41,42]
Summary
Alternaria brassicicola is a destructive plant pathogen and causes black spot disease on almost all plant species in the Brassicaceae [1,2,3]. Disease symptoms appear mainly on the leaves and stems of host plants, including Brassica oleracea (vegetables), B. rapa (vegetables, oilseeds, and forages), B. juncea (vegetables and seed mustard), the vegetable oil-producing species B. napus (oilseeds) [4], and the model plant Arabidopsis thaliana [5]. This disease is of worldwide economic importance [1,2,3,6,7] and can result in 20 to 50% yield reductions in crops such as canola and rape [7]. It has been suspected that toxins and CAZys play important roles in pathogenesis [15], we are still searching for genes whose loss-of-function mutation causes a reduction in virulence
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call