Plant Responses of Maize to Two formae speciales of Sporisorium reilianum Support Recent Fungal Host Jump.

Host jumps are a major factor for the emergence of new fungal pathogens. In the evolution of smut fungi, a putative host jump occurred in Sporisorium reilianum that today exists in two host-adapted formae speciales, the sorghum-pathogenic S. reilianum f. sp. reilianum and maize-pathogenic S. reilianum f. sp. zeae. To understand the molecular host-specific adaptation to maize, we compared the transcriptomes of maize leaves colonized by both formae speciales. We found that both varieties induce many common defense response-associated genes, indicating that both are recognized by the plant as pathogens. S. reilianum f. sp. reilianum additionally induced genes involved in systemic acquired resistance. In contrast, only S. reilianum f. sp. zeae induced expression of chorismate mutases that function in reducing the level of precursors for generation of the defense compound salicylic acid (SA), as well as oxylipin biosynthesis enzymes necessary for generation of the SA antagonist jasmonic acid (JA). In accordance, we found reduced SA levels as well as elevated JA and JA-Ile levels in maize leaves inoculated with the maize-adapted variety. These findings support a model of the emergence of the maize-pathogenic variety from a sorghum-specific ancestor following a recent host jump.

Genome-wide identification, characterization, and expression profiling of SPX gene family in wheat.

The SPX gene family, ubiquitous in all vascular plants, plays a critical role in plant development and growth as well as in response to phosphorus stress. Based on genomic census, 46 TaSPX genes were identified in the wheat genome. All of them are evenly distributed on 13 of the 21 wheat chromosomes and chromosome 7A contains the largest members. As many as 57 gene specific SSRs were discovered among genomic sequences of identified TaSPXs. MicroRNA target analysis revealed that TaSPX genes were targeted by 9 different miRNAs including tae-miR1120a, tae-miR1120b-3p, tae-miR1120c-5p, tae-miR1122b-3p, tae-miR1122c-3p, tae-miR1130a, tae-miR1130b-3p, tae-miR1137a, and tae-miR1137b-5p. Expression profiles derived from transcriptome data and real-time quantitative PCR revealed that TaSPX genes were significantly induced by Pi starvation. The modeled 3D structure of wheat SPX proteins shared high level of homology with template structures, providing information to understand their functions at proteomic level. We have also refined the modeled 3D structures on 10 ns using molecular dynamics simulations for conformational stability. The discovered members of SPX gene family and their targeting miRNAs may provide resource for genetic improvement and promote P use efficiency in cereals.