In self-incompatible (SI) plants, the S locus acts to prevent growth of self-pollen and thus promotes outcrossing within the species. lnterspecific crosses between SI and self-compatible (SC) species often show unilateral lncompatibility that follows the S I x SC rule: S I specles reject pollen from SC specles, but the reciproca1 crosses are usually compatible. The general validity of the S I x SC rule suggests a link between S I and interspeclflc pollen rejectlon; however, this link has been questioned because of a number of exceptlons to the rule. To clarlfy the role of the S locus in interspecific pollen rejection, we transformed severa1 Nicotlana species and hybrids with genes encodlng S A~ or SC,O RNase from S I N. alata. Compatibillty phenotypes in the transgenlc plants were tested using pollen from three SC specles showing unilateral incompatibility with N. alata. S RNase was lmpllcated ln rejecting pollen from all three specles. Rejection of N. plumbaginifolia pollen was similar to S allele-speclfic pollen rejection, showing a requirement for both S RNase and other genetic factors from N. alata. In contrast, S RNase-dependent rejectlon of N. glutinosa and N. tabacum pollen proceeded without these additional factors. N. alata also rejects pollen fmm the latter two specles through an S RNaseindependent mechanism. Our results lmplicate the S locus in all three systems, but lt 1s clear that multlple mechanisms contribute to interspecific pollen rejectlon. INTRODUCTIONMany plants have evolved genetically controlled selfincompatibility (SI) systems that promote outcrossing by restricting pollination between closely related individuals of the same species (de Nettancourt, 1977). Mechanisms also exist to restrict pollination between different species, but comparatively little is known about the control of interspecific pollination.As in other solanaceous plants, SI in the genus Nicotiana is controlled by a single multiallelic locus, the S locus (Newbigin et al., 1993). These plants employ a gametophytic SI system in which pollen is rejected if the S allele in the haploid pollen is the same as either S allele in the diploid pistil. S allele-specific pollen rejection occurs as pollen tubes grow through the extracellular matrix of the stylar transmitting tract (Newbigin et al., 1993). The products of the S locus in the style are the To whom correspondence should be addressed.S RNases (McClure et al., 1989). These glycoproteins are very abundant in the extracellular matrix of the transmitting tract and are also expressed in the stigma and in the epidermis of the placenta (Cornish et Anderson et al., 1989;McClure et al., 1993). S RNases are essential for S allele-specific pollen rejection Murfett et al., 1994), and their ribonuclease activity is required for this function . Following incompatible pollinations, RNA in selfpollen tubes is degraded, and this degradation is consistent with a cytotoxic model for pollen rejection (McClure et al., 1990;Gray et al., 1991; Dickinson, 1994). SI is therefore an active process i...

Wheat grain is sold based upon several physiochemical characteristics, one of the most important being grain texture. Grain texture in wheat directly affects many end use qualities such as milling yield, break flour yield, and starch damage. The hardness (Ha) locus located on the short arm of chromosome 5D is known to control grain hardness in wheat. This locus contains the puroindoline A ( pina) and puroindoline B ( pinb) genes. All wheats to date that have mutations in pina or pinb are hard textured, while wheats possessing both the 'soft type' pina-D1a and pinb-D1a sequences are soft. Furthermore, it has been shown that complementation of the pinb-D1b mutation in hard spring wheat can restore a soft phenotype. Here, our objective was to identify and characterize the effect the puroindoline genes have on grain texture independently and together. To accomplish this we transformed a hard red spring wheat possessing a pinb-D1b mutation with 'soft type' pina and pinb, creating transgenic isolines that have added pina, pinb, or pina and pinb. Northern blot analysis of developing control and transgenic lines indicated that grain hardness differences were correlated with the timing of the expression of the native and transgenically added puroindoline genes. The addition of PINA decreased grain hardness less than the reduction seen with added PINB. Seeds from lines having more 'soft type' PINB than PINA were the softest. Friabilin abundance was correlated with the presence of both 'soft type' PINA and PINB and did not correlate well with total puroindoline abundance. The data indicates that PINA and PINB interact to form friabilin and together affect wheat grain texture.

Genetic diversity is the basis for successful crop improvement and can be estimated by different methods. The objectives of this study were to estimate the genetic diversity of 30 ancestral to modern hard red winter wheat (Triticum aestivum L.) cultivars adapted to the Northern Great Plains using pedigree information, morphological traits (agronomic measurements from six environments), end-use quality traits (micro-quality assays on 50 g grain or milled flour samples for the six environments), and molecular markers (seed storage proteins separated using SDS-PAGE, 51 SSRs, and 23 SRAP DNA markers), and to determine the relationships of genetic distance estimates obtained from these methods. Relationships among diversity estimates were determined using simple (Pearson) and rank (Spearman) correlation coefficients between distance estimates and by clustering cultivars using geneticdistances for different traits. All methods found a wide range in genetic diversity. The genetic distance estimates based on pedigree had the highest values due to possible over-estimation arising from model assumptions. The genetic diversity estimates based on seed storage protein were lowest because they were the major determinants of end-use quality, which is a highly selected trait. In general, the diversity estimates from each of the methods were positively correlated at a low level with the exceptions of SRAP diversity estimates being independent of morphologic traits (simple correlation), SDS-PAGE, and SSR diversity estimates (rank correlation). However, SSR markers, thought to be among the most efficient markers for estimating genetic diversity, were most highly correlated with seed storage proteins. The procedures used to accurately estimate genetic diversity will depend largely upon the tools available to the researcher and their application to the breeding scheme.