Analysis of QTLs and Candidate Genes for Tassel Symptoms in Maize Infected with Sporisorium reilianum

Abstract

Heat smut is a fungal soil-borne disease caused by Sporisorium reilianum, and affects the development of male and female tassels. Our previous research found that the tassel symptoms in maize infected with Sporisorium reilianum significantly differed in inbred lines with Sipingtou blood, and exhibited stable heredity over time at multiple locations. In this study, cytological analysis demonstrated that the cellular organization structures of three typical inbred lines (Huangzao4, Jing7, and Chang7-2) showed significant discrepancies at the VT stage. QTLs that control the different symptoms of maize tassels infected with Sporisorium reilianum were located in two F2 populations, which were constructed using three typical inbred lines. The BSA (bulked segregation analysis) method was used to construct mixed gene pools based on typical tassel symptoms. The QTLs of different symptoms of maize tassels infected with Sporisorium reilianum were detected with 869 SSR markers covering the whole maize genome. The mixed gene pools were screened with polymorphic markers between the parents. Additional SSR markers were added near the above marker to detect genotypes in partially single plants in F2 populations. The QTL controlling tassel symptoms in the Huangzao4 and Jing7 lines was located on the bin 1.06 region, between the markers of umc1590 and bnlg1598, and explained 21.12% of the phenotypic variation with an additive effect of 0.6524. The QTL controlling the tassel symptoms of the Jing7 and Chang7-2 lines was located on the bin 2.07 region, between the markers of umc1042 and bnlg1335, and explained 11.26% phenotypic variation with an additive effect of 0.4355. Two candidate genes (ZmABP2 and Zm00001D006403) were identified by a conjoint analysis of label-free quantification proteome sequencings.

Physiological Mechanisms Underlying Tassel Symptom Formation in Maize Infected with Sporisorium reilianum

“…Previous research from our lab found that maize tassel symptoms primarily occur during the V12–VT stages, during which the cellular structure is completely destroyed and visible teliospores form in the diseased tissues of Huangzao4 and Chang7-2 plants. In Jing7, the cellular contents disappear completely, with only the cell wall remaining and an absence of visible teliospores [ 39 ]. Teliospore formation may be induced by host secretions and can damage host cells; thus, differences in teliospore abundance may underlie line-specific differences in tassel symptoms.…”

“…In a previous study, we found key changes at the V12–VT stage in the inbred lines Huangzao4 and Chang7-2 (cell wall disintegration and intracellular spore production) and Jing7 (complete loss of cell contents with only the cell wall remaining). Spore formation may be induced by host secretions but can cause damage to host cell walls, enabling further pathogen invasion into the plant [ 39 ]. Plant–pathogen interactions lead to a variety of changes in host defense-related enzymes and hormone contents.…”