Brown‐midrib maize (bm1) – a mutation affecting the cinnamyl alcohol dehydrogenase gene

Brown-midrib (bm) mutants of maize have modified lignin of reddish-brown colour. Although four independent bm loci are known, only one of the mutant genes has been previously identified. We report here that maize bm1, one of the less characterised mutants, shows severely reduced CAD activity in lignified tissues, resulting in the production of a modified lignin. Both the total lignin content and the structure of the polymer are altered by the mutation. We further describe the isolation and characterisation of the maize CAD cDNA and mapping of the CAD gene. CAD maps very closely to the known location of bm1 and co-segregates with the bm1 locus in two independent recombinant inbred populations. These data strongly support the premise that maize bm1 directly affects expression of the CAD gene.     

Mapping QTL controlling yield and yield components in a spring barley (Hordeum vulgare L.) cross using marker regression

An RFLP map constructed from 99 doubled haploid lines of a cross between two spring barley varieties (Blenheim × Kym) was used to localize quantitative trait loci (QTL) controlling grain yield and yield components by marker regression and single-marker analysis. Trials were conducted over three years. Genotype-by-year interaction was detected for plant grain weight and ear grain weight so they were analysed separately for each year. None was detected for thousand-grain weight and ear grain number so data were pooled over years. A total of eleven QTL were detected for plant grain weight over two years and fourteen for ear grain weight over three years. Seven QTL were detected for plot yield. The locus with the largest effect was on chromosome 2(2H)L and accounted for 19% of the variation in the progeny. Eight QTL were detected for thousand-grain weight and five for ear grain number. Many of the QTL detected were in comparable positions in each year. Yield and yield components were only partly correlated. Comparisons based on common RFLP markers showed that some QTL were found in positions similar to those identified in other studies. For a number of QTL the identification of linked markers provided suitable opportunities for marker-assisted selection and improvement of barley and reference markers with which to analyse the homoeologous chromosome regions of wheat and other cereals.     

Some practical considerations for using RFLP markers to aid in selection during inbreeding of maize

Summary If molecular markers are to be routinely used in maize (Zea mays L.) breeding for selection of quantitative trait loci (QTL), then consistent marker-trait associations across breeding populations are needed, as are efficient methods for weighting information from different markers. Given 15 restriction fragment length polymorphism (RFLP) markers associated with grain yield in testcrosses of 220 [BS11(FR)C7 x FRMol7] F₂ individuals to FRB73, separate weighting schemes were attempted in order to maximize the frequency of favorable marker genotypes associated with increased grain yield in selected F₂ individuals and F₂:S₄ Unes. The following principles were apparent: (1) Differential weighting among markers, in addition to weighting individual marker genotypes on the basis of associated mean effects, should be emphasized when using markers to select in breeding populations. This is due to limited population sizes that can readily be handled. (2) Relatively few markers may need to be used to screen segregating populations (e.g., F₂) of limited size for loci affecting complex traits, such as combining ability for grain yield, assuming prior knowledge of marker-QTL associations. Markers given greatest weight (largest estimates of associated effects) will determine most selections. (3) When marker-based selection is among individuals at higher levels of inbreeding (e.g., S₄) within selected families, more markers need to be used in screening because those associated with relatively small effects have an increased chance of affecting selection.These results suggest a qualitative approach for utilizing RFLP markers to aid in selection of complex traits in commercial hybrid maize breeding programs. Commercial research programs produce thousands of crosses each year aimed at inbred line development. Discovery of molecular markers with consistent QTL associations across breeding populations and close QTL linkages would allow for rapid screening of new F₂ populations at a few key markers. Early elimination of individuals with undesirable genotypes would reduce the extent of hybrid performance testing necessary during later stages of inbreeding.     

Sequencing,expression pattern and RFLP mapping of a senescence-enhanced cDNA from Zea mays with high homology to oryzain γ and aleurain

Sequence analysis of a 1.4 kb clone from a cDNA library of senescing Zea mays leaves reveals an open reading frame for a 360 amino acid protein. Both the DNA and deduced amino acid sequences are highly homologous to the cysteine proteinases oryzain and aleurain. Northern analysis demonstrates that the corresponding RNA level increases during natural leaf senescence, seedling germination and in chilling of tolerant maize lines, but decreases in a sensitive line. The mRNA level also decreases in regreening leaves, in dark-induced senescence and in nutrient or water stress. Southern and RFLP analysis provide evidence that the gene has two copies, on chromosomes 2 and 7.     

Effect of carbohydrate source on alpha-amylase and glucoamylase formation byClostridium acetobutylicum SA-1

Summary An examination into the effect of different carbohydrate sources indicated that the production of extracellular alpha-amylase and glucoamylase was under similar biosynthetic control inClostridium acetobutylicum SA-1. Cell-associated starch-hydrolytic enzymes may be more important than extracellular enzymes in the processing of the starch molecule.