Heterologous Overexpression of Arabidopsis cel1 Enhances Grain Yield, Biomass and Early Maturity in Setaria viridis

Heterologous overexpression of Arabidopsis cellulase 1 (Atcel1) results in enhanced yield, early maturity, and increased biomass in dicotyledonous species like poplar and eucalyptus but has not been demonstrated in monocots. We produced transgenic Setaria viridis accession A10.1 plants overexpressing a monocotyledonous codon optimized (MCO) Atcel1. Agronomic characterization of the transgenic events showed that heterologous overexpression of MCOAtcel1 caused enhanced grain yield, shoot biomass, and accelerated maturation rate in the model grass species S. viridis under growth chamber conditions. The agronomic trait differences observed were consistent with previous reports in dicots but are here described in a monocot species and associated with increased seed yield. Overexpression of Atcel1 in S. viridis was shown to increase the number of panicles and seeds by 24-30%, enhance overall grain yield by up to 26%, and lead to a shoot dry biomass increase of 16-19%. Overexpression also reduced time to plant maturation and senescence by 12.5%. Our findings in S. viridis suggest that manipulation of Atcel1 has potential for developing early-maturing and higher-yielding monocotyledonous biomass crops suitable for climate-smart agriculture.

A genome-wide association study of the maize hypersensitive defense response identifies genes that cluster in related pathways

Much remains unknown of molecular events controlling the plant hypersensitive defense response (HR), a rapid localized cell death that limits pathogen spread and is mediated by resistance (R-) genes. Genetic control of the HR is hard to quantify due to its microscopic and rapid nature. Natural modifiers of the ectopic HR phenotype induced by an aberrant auto-active R-gene (Rp1-D21), were mapped in a population of 3,381 recombinant inbred lines from the maize nested association mapping population. Joint linkage analysis was conducted to identify 32 additive but no epistatic quantitative trait loci (QTL) using a linkage map based on more than 7000 single nucleotide polymorphisms (SNPs). Genome-wide association (GWA) analysis of 26.5 million SNPs was conducted after adjusting for background QTL. GWA identified associated SNPs that colocalized with 44 candidate genes. Thirty-six of these genes colocalized within 23 of the 32 QTL identified by joint linkage analysis. The candidate genes included genes predicted to be in involved programmed cell death, defense response, ubiquitination, redox homeostasis, autophagy, calcium signalling, lignin biosynthesis and cell wall modification. Twelve of the candidate genes showed significant differential expression between isogenic lines differing for the presence of Rp1-D21. Low but significant correlations between HR-related traits and several previously-measured disease resistance traits suggested that the genetic control of these traits was substantially, though not entirely, independent. This study provides the first system-wide analysis of natural variation that modulates the HR response in plants.

The hypersensitive pathogen defense response (HR) in plants typically consists of a rapid, localized cell death around the point of attempted pathogen penetration. It is found in all plant species and is associated with high levels of resistance to a wide range of pathogens and pests including bacteria, fungi, viruses, nematodes, parasitic plants and insects. Little is known about the control of HR after initiation, largely because it is so rapid and localized and therefore difficult to quantify. Here we use a mutant maize gene conferring an exaggerated HR to quantify HR levels in a set of 3,381 mapping lines characterised at 26.5 million loci to identify genes associated with naturally-occurring variation in HR. Many of these genes seem to be involved in a set of connected regulatory pathways including protein degradation, control of programmed cell death, recycling of cellular components and regulation of oxidative stress. We have also shown that several of these genes show high levels of expression induction during HR. The study provides the first comprehensive list of natural variants in maize genes that modulate HR and cluster within reported pathways underlying molecular events during HR.

Genetic mapping of adult plant leaf rust resistance genes Lr48 and Lr49 in common wheat

Hypersensitive adult plant resistance genes Lr48 and Lr49 were named based on their genetic independence of the known adult plant resistance genes. This study was planned to determine genomic locations of these genes. Recombinant inbred line populations derived from crosses involving CSP44 and VL404, sources of Lr48 and Lr49, respectively, and the susceptible parent WL711, were used to determine the genomic locations of these genes. Bulked segregant analyses were performed using multiplex-ready PCR technology. Lr48 in genotype CSP44 was mapped on chromosome arm 2BS flanked by marker loci Xgwm429b (6.1 cM) and Xbarc7 (7.3 cM) distally and proximally, respectively. Leaf rust resistance gene Lr13, carried by the alternate parent WL711, was proximal to Lr48 and was flanked by Xksm58 (5.1 cM) and Xstm773-2 (8.7 cM). Lr49 was flanked by Xbarc163 (8.1 cM) and Xwmc349 (10.1 cM) on chromosome arm 4BL. The likely presence of the durable leaf rust resistance gene Lr34 in both CSP44 and VL404 was confirmed using the tightly linked marker csLV34. Near-isogenic lines for Lr48 and Lr49 were developed in cultivar Lal Bahadur. Genotypes combining Lr13 and/or Lr34 with Lr48 or Lr49 were identified as potential donor sources for cultivar development programs.