Brown midrib mutant and genome‐wide association analysis uncover lignin genes for disease resistance in maize

Abstract

Brown midrib (BMR) maize (Zea mays L.) harbors mutations that result in lower lignin levels and higher feed digestibility, making it a desirable silage market class for ruminant nutrition. Northern leaf blight (NLB) epidemics in upstate New York highlighted the disease susceptibility of commercially grown BMR maize hybrids.We found the bm1, bm2, bm3, and bm4 mutants in a W64A genetic background to be more susceptible to foliar fungal (NLB, gray leaf spot [GLS], and anthracnose leaf blight [ALB]) and bacterial (Stewart's wilt) diseases. The bm1, bm2, and bm3 mutants showed enhanced susceptibility to anthracnose stalk rot (ASR), and the bm1 and bm3 mutants were more susceptible to Gibberella ear rot (GER). Colocalization of quantitative trait loci (QTL) and correlations between stalk strength and disease traits in recombinant inbred line families suggest possible pleiotropies. The role of lignin in plant defense was explored using high-resolution, genome-wide association analysis for resistance to NLB in the Goodman diversity panel. Association analysis identified 100 single and clustered single-nucleotide polymorphism (SNP) associations for resistance to NLB but did not implicate natural functional variation at bm1-bm5. Strong associations implicated a suite of diverse candidate genes including lignin-related genes such as a β-glucosidase gene cluster, hct11, knox1, knox2, zim36, lbd35, CASP-like protein 8, and xat3. The candidate genes are targets for breeding quantitative resistance to NLB in maize for use in silage and nonsilage purposes.

Genome-wide identification of the CAD gene family and functional analysis of putative bona fide CAD genes in tobacco (Nicotiana tabacum L.)

“…CAD -deficient plants display a brown midrib phenotype, characterized by a distinct reddish-brown color and altered lignin biosynthesis. This phenotypic variation has been observed in several plant species, including rice ( Zhang et al., 2006 ), maize ( Halpin et al., 1998 ; Kolkman et al., 2023 ), sorghum ( Sattler et al., 2009 ; Rivera-Burgos et al., 2019 ), poplar ( Baucher et al., 1996 ), and mulberry ( Chao et al., 2022 ). This change in stem color is attributed to the accumulation or enrichment of coniferyl aldehydes ( Li et al, 2008b ).…”

Moisture relationships among conventional and brown‐midrib corn hybrids for silage

“…The moisture content goal for initiating corn silage harvest is typically 68% moisture and is difficult to assess in the field without a moisture analysis, but moisture assessment in the field is essential to achieve the correct harvest timing for proper ensiling. Although brown‐midrib (BMR) corn hybrids are higher in nutritive value compared to conventional (CONV) types (Ferraretto & Shaver, 2015; Saunders et al., 2015), BMR hybrids can be very susceptible to disease (Kolkman et al., 2020; Reed et al., 2021), making moisture estimation in the field by visual examination extremely difficult. Diseased plants often lose all visible green coloring prior to harvest (Cherney & Cox, 2020; Kolkman et al., 2020).…”

“…Although brown‐midrib (BMR) corn hybrids are higher in nutritive value compared to conventional (CONV) types (Ferraretto & Shaver, 2015; Saunders et al., 2015), BMR hybrids can be very susceptible to disease (Kolkman et al., 2020; Reed et al., 2021), making moisture estimation in the field by visual examination extremely difficult. Diseased plants often lose all visible green coloring prior to harvest (Cherney & Cox, 2020; Kolkman et al., 2020).…”