A New SNP in Rice Gene Encoding Pyruvate Phosphate Dikinase (PPDK) Associated with Floury Endosperm

Rice varieties with suitable flour-making qualities are required to promote the rice processed-food industry and to boost rice consumption. A rice mutation, Namil(SA)-flo1, produces grains with floury endosperm. Overall, grains with low grain hardness, low starch damage, and fine particle size are more suitable for use in flour processing grains with waxy, dull endosperm with normal grain hardness and a high amylose content. In this study, fine mapping found a C to T single nucleotide polymorphism (SNP) in exon 2 of the gene encoding cytosolic pyruvate phosphate dikinase (cyOsPPDK). The SNP resulted in a change of serine to phenylalanine acid at amino acid position 101. The gene was named FLOURY ENDOSPERM 4-5 (FLO4-5). Co-segregation analysis with the developed cleaved amplified polymorphic sequence (CAPS) markers revealed co-segregation between the floury phenotype and the flo4-5. This CAPS marker could be applied directly for marker-assisted selection. Real-time RT-PCR experiments revealed that PPDK was expressed at considerably higher levels in the flo4-5 mutant than in the wild type during the grain filling stage. Plastid ADP-glucose pyrophosphorylase small subunit (AGPS2a and AGPS2b) and soluble starch synthase (SSIIb and SSIIc) also exhibited enhanced expression in the flo4-5 mutant.

A carbohydrate-binding protein, FLOURY ENDOSPERM 6 influences the initiation of A- and B-type starch granules in wheat

Previously, we identified a quantitative trait locus on the group 4 chromosomes of Aegilops and bread wheat that controls B-type starch-granule content. Here, we identify a candidate gene by fine-mapping in Aegilops and confirm its function using wheat TILLING mutants. This gene is orthologous to the FLOURY ENDOSPERM 6 (FLO6) gene of rice and barley and the PTST2 gene of Arabidopsis. In Triticeae endosperm, reduction in the gene dose of functional FLO6 alleles results in reduction, or loss, of B-granules. This is due to repression of granule initiation in late-grain development, but has no deleterious impact on the synthesis of A-granules. The complete absence of functional FLO6, however, results in reduced numbers of normal A-type and B-type granules and the production of highly-abnormal granules that vary in size and shape. This polymorphous starch seen in a wheat flo6 triple mutant is similar to that observed in the barley mutant Franubet. Analysis of Franubet (fractured Nubet) starch suggests that the mutant A-granules are not fractured but compound, due to stimulation of granule initiation in plastids during early-grain development. Thus, in different situations in Triticeae, FLO6 either stimulates or represses granule initiation.

Moisture and Rupture Models for Corn (Zea mays) Seeds of Different Endosperm Types

Mechanization of postharvest handling and conditioning inflicts damage on the physical, physiological, and sanitary qualities of corn (Zea mays) seeds, resulting in significant economic loss. The mechanical damage is related to the compression strength and strain, and therefore to the moisture content (MC) and endosperm type. This study was conducted from 2012 to 2014 at the Montecillo and Chapingo agricultural institutes in Mexico, where physical properties such as volumetric weight; apparent density; rupture compression strength, strain, and energy; and endosperm type were evaluated for five corn seed cultivars (floury, semi-floury, floury-flint, semi-flint, and flint) at seven MC levels (8%, 12%, 16%, 20%, 24%, 28%, and 32% w.b.). The aim of this study was to develop moisture-strength, moisture-strain, and moisture-energy regression models for postharvest handling of corn to prevent quality loss due to mechanization. For three model groups, the relationship (1) between MC and rupture strain was linear and directly proportional for the five studied cultivars; (2) between MC and rupture strength was linear and directly proportional for the floury cultivar, inverse for the semi-flint and flint cultivars, and quadratic for the semi-floury and floury-flint cultivars; and (3) between MC and rupture energy was linear and directly proportional for the floury cultivar and quadratic for the semi-floury, floury-flint, semi-flint, and flint cultivars. The models obtained in this study might be used as a reference for better handling of corn seeds, as none of the five studied varieties had a uniformly superior rupture strength, strain, or energy at the studied MC levels. Floury endosperm types might be handled at high MC and flint endosperm types might be handled at low MC to avoid mechanical damage produced by static loads; both types of endosperm support greater energy loads, e.g., impact, at higher MC. Keywords: Compression, Corn quality, Flint endosperm, Floury endosperm, Moisture, Zea mays.