Dick L. Auld

Expression of an Arabidopsis vacuolar H+-pyrophosphatase gene (AVP1) in cotton improves drought- and salt tolerance and increases fibre yield in the field conditions

The Arabidopsis gene AVP1 encodes a vacuolar pyrophosphatase that functions as a proton pump on the vacuolar membrane. Overexpression of AVP1 in Arabidopsis, tomato and rice enhances plant performance under salt and drought stress conditions, because up-regulation of the type I H+-PPase from Arabidopsis may result in a higher proton electrochemical gradient, which facilitates enhanced sequestering of ions and sugars into the vacuole, reducing water potential and resulting in increased drought- and salt tolerance when compared to wild-type plants. Furthermore, overexpression of AVP1 stimulates auxin transport in the root system and leads to larger root systems, which helps transgenic plants absorb water more efficiently under drought conditions. Using the same approach, AVP1-expressing cotton plants were created and tested for their performance under high-salt and reduced irrigation conditions. The AVP1-expressing cotton plants showed more vigorous growth than wild-type plants in the presence of 200 mM NaCl under hydroponic growth conditions. The soil-grown AVP1-expressing cotton plants also displayed significantly improved tolerance to both drought and salt stresses in greenhouse conditions. Furthermore, the fibre yield of AVP1-expressing cotton plants is at least 20% higher than that of wild-type plants under dry-land conditions in the field. This research indicates that AVP1 has the potential to be used for improving crops drought- and salt tolerance in areas where water and salinity are limiting factors for agricultural productivity.

Development of Castor with Reduced Toxicity

ABSTRACT Two approaches are being used to develop castor (Ricinus communis L.) cultivars with reduced levels of toxin. Conventional sexual hybridization was used to develop F6 lines of castor that have a 75-70% reduction in ricin + RCA toxins. The plants will be combined with transgenic castor plants which have a potential for > 99% reduction in ricin content. Subsequent selection in segregating generations should provide a 99.9% reduction in protein toxins allowing development of a very low toxin (VLT) castor cultivars. These cultivars would allow production of castor in the U.S. while increasing the value of the high protein meal remaining after extraction of the castor oil.

Inheritance of fiber quality and lint yield in a chemically mutated population of cotton

The narrow germplasm base of the upland cotton (Gossypium hirsutum L.), grown on the Texas high plains historically, has limited improvement of fiber quality. Chemical mutagenesis and subsequent selection have helped the development of lines with improved fiber quality in cultivars adapted to this region. This study was conducted to determine the inheritance of improvements in fiber quality. M3 lines with divergent fiber properties of micronaire, length, and strength were selected from a population of Paymaster HS 200 treated with 3% v/v ethyl methanesulfonate (EMS) for two hours. The 115 selected lines of M4 and M5 generation were evaluated for fiber quality and lint yield. Regression of the M4 and M5 on the M3 generation, as well as the M5 on the M4 was used to generate narrow sense heritability coefficients. Significant variations were observed between the mutant lines in all generations except for lint yield in the M5 (1997). The highest heritability estimates were found in fiber length (h2= 0.29** to 0.46**). Micronaire and strength showed intermediate heritability estimates of h2= 0.14 to 0.19, while lint yield had a very low heritability estimate of h2= 0.03. Fiber length and strength were correlated (r= 0.58** to 0.46**) in all the three generations. The mutants identified in these studies have the potential to improve fiber quality of upland cotton without introducing alien genes that may reduce adaptation to short growing season production regions.

Development of ‘naked-tufted’ seed coat mutants for potential use in cotton production

Use of chemical mutagenesis has been highly successful in most major crops. The objective of this research was to develop ‘naked-tufted’ seed mutants and to incorporate this genetic trait into cotton to enhance crop quality and reduce processing costs. In 1997, six commercial cultivars were treated with 2.45% v/v ethyl methane sulfonate. In 1999, three M3 plants were identified that had partially naked seed coats. The trait was stabilized through individual plant selections from 2000 to 2004. During 2005 and 2006, the homozygous naked-tufted M8 mutant lines were evaluated for lint yield, lint percent, fibers/seed, fibers/mm2, fiber quality, seed oil content, ginning efficiency and yarn spinning performance. Overall, the naked-tufted seed mutants had lower lint yield, lower fibers/seed, lower lint/seed, and lower fibers/mm2 when compared with their original fuzzy parents. The lint turnout from the mutants was similar to the fuzzy parents and the commercial cultivars. The naked-tufted seed mutants had higher seed oil percent, 6–17% lower short fiber contents, significantly reduced seed coat neps (37–42%), higher elongation and yarn tenacity than their fuzzy counterparts. Preliminary data also showed that the naked-tufted mutants required less energy to gin.

Overexpression of the Rice SUMO E3 Ligase Gene OsSIZ1 in Cotton Enhances Drought and Heat Tolerance, and Substantially Improves Fiber Yields in the Field under Reduced Irrigation and Rainfed Conditions

The Arabidopsis SUMO E3 ligase gene AtSIZ1 plays important roles in plant response to abiotic stresses as loss of function in AtSIZ1 leads to increased sensitivity to drought, heat and salt stresses. Overexpression of the AtSIZ1 rice homolog, OsSIZ1, leads to increased heat and drought tolerance in bentgrass, suggesting that the function of the E3 ligase SIZ1 is highly conserved in plants and it plays a critical role in abiotic stress responses. To test the possibility that the SUMO E3 ligase could be used to engineer drought- and heat-tolerant crops, the rice gene OsSIZ1 was overexpressed in cotton. We report here that overexpression of OsSIZ1 in cotton results in higher net photosynthesis and better growth than wild-type cotton under drought and thermal stresses in growth chamber and greenhouse conditions. Additionally, this tolerance to abiotic stresses was correlated with higher fiber yield in both controlled-environment and field trials carried out under reduced irrigation and rainfed conditions. These results suggest that OsSIZ1 is a viable candidate gene to improve crop yields under water-limited and rainfed agricultural production systems.

Alleles conferring improved fiber quality from EMS mutagenesis of elite cotton genotypes

Key messageGenetic improvements for many fiber traits are obtained by mutagenesis of elite cottons, mitigating genetic uniformity in this inbred polyploid by contributing novel alleles important to ongoing crop improvement.AbstractThe elite gene pool of cotton (Gossypium spp.) has less diversity than those of most other major crops, making identification of novel alleles important to ongoing crop improvement. A total of 3,164 M5 lines resulting from ethyl methanesulfonate (EMS) mutagenesis of two G. hirsutum breeding lines, TAM 94L-25 and Acala 1517-99, were characterized for basic components of fiber quality and selected yield components. Across all measured traits, the ranges of phenotypic values among the mutant lines were consistently larger than could be explained by chance (5.27–10.1 for TAM 94 L-25 and 5.29–7.94 standard deviations for Acala 1517-99-derived lines). Multi-year replicated studies confirmed a genetic basis for these differences, showing significant correlations between lines across years and environments. A subset of 157 lines selected for superior fiber qualities, including fiber elongation (22 lines), length (22), lint percent (17), fineness (23), Rd value (21), strength (19), uniformity (21) and multiple attributes in a selection index (26) were compared to 55 control lines in replicated trials in both Texas and Georgia. For all traits, mutant lines showing substantial and statistically significant improvements over control lines were found, in most cases from each of the two genetic backgrounds. This indicates that genetic improvements for a wide range of fiber traits may be obtained from mutagenesis of elite cottons. Indeed, lines selected for one fiber trait sometimes conferred additional attributes, suggesting pleiotropic effects of some mutations and offering multiple benefits for the incorporation of some alleles into mainstream breeding programs.

The inheritance of a basal branching type in guar

Conflicting theories of inheritance of branching in guar [Cyamopsis tetragonoloba (L.) Taub.] have been reported. In this study, two lines differing in leaf surface and growth habit were used to make reciprocal crosses and form progeny populations in order to study how basal branching is inherited. Parents in the reciprocal crosses were PI 217923, which is an erect type with pubescent leaves that exhibits predominantly zero, but as many as four basal branches; and ‘Lewis’, which is a branching type with glabrous leaves that exhibits from two to ten branches at the base. Parental and progeny populations were evaluated for branching under field-grown conditions. Effect of plant spacing (seeding rate at 1 seed/cm vs. 1 seed/30 cm) on basal branching of PI 217923 and Lewis was studied. Hybrids were identified by erect branching and pubescent leaf surface. F1 plants had erect branching type and pubescent leaves, indicating that erect branching is dominant to basal branching and there is no maternal effect. Chi-square goodness-of-fit analysis revealed that F2 populations segregated in the expected 3:1 ratio (P<0.10–0.70), indicating that basal branching was controlled by one gene. We propose gene symbol Brh-1 for the gene that controls lack of branching as in segregating populations, Brh-1 is dominant to brh-1. Thus, the genotype of PI 217923 would be Brh-1/Brh-1 or Brh-1/brh-1 as it exhibits erect growth habit with little branching, while that of Lewis would be brh-1/brh-1. When grown at wider plant spacing (1 seed/30 cm), all branching increased, but 3 or 4 basal branches appeared in PI 217923, while the average number of basal branches in Lewis increased from 4.0 to 8.4.

Mutagenesis Systems for Genetic Analysis of Gossypium

The recent evolution of tetraploid cotton combined with intensive selection of cultivated cottons has reduced the genetic diversity of cotton. This lack of allelic diversity hampers efforts to improve the agronomic traits of cotton and limits the application of molecular genetic tools for improvement of cotton germplasm. The lack of genetic resources also reduces our ability to understand the molecular mechanisms that regulate cotton growth and development and its responses to environmental stresses and pathogens. Use of a variety of chemical mutagens and ionizing radiation can be used to effectively increase the frequency of mutant alleles in Gossypium species. While application of insertional mutagenesis methodologies that require high-throughput plant transformation procedures is not feasible, evaluation of various transposon-based mutagenesis systems is underway. TILLING technology, which uses a combination of mutagenesis and high-throughput molecular screening methods for reverse genetics is also being developed.

The Inheritance and Variation of Gum Content in Guar [Cyamopsis tetragonoloba (L.) Taub.]

Abstract Guar [Cyamopsis tetragonoloba (L.) Taub.] is one of the most important industrial crops due to its richness in gum. Understanding the inheritance of gum content is a key to its successful genetic improvement. Gum content expression is reported to be controlled by additive, dominant, and epistatic effects, and modified by the environment. fg%, a relative gum content calculated by comparing with the gum content of Kinman was used as gum content (%) in this experiment. Reciprocal crosses of two lines of guar, PI 217923 and Lewis, were made to study the heritability of gum content (fg%). fg% of four plant introductions and four commercial varieties were studied in Lubbock in 1999–2002. Estimates of broad-sense heritability (h2 b.s.) of fg% in Lewis × PI 217923 and PI 217923 × Lewis were 75.53 and 52.74%, respectively. Estimates of narrow-sense heritability (h2 n.s.) of fg% were 40.00 and 29.00% for Lewis × PI 217923 and PI 217923× Lewis, respectively. At least one pair of genes were estimated to control the fg% expression in these two crosses. Significant differences of fg% were found among these eight entries. PI 217923 was found to have the highest fg% among the eight entries.