No abstract

Crop yield is a highly complex quantitative trait. Historically, successful breeding for improved grain yield has led to crop plants with improved source capacity, altered plant architecture, and increased resistance to abiotic and biotic stresses. To date, transgenic approaches towards improving crop grain yield have primarily focused on protecting plants from herbicide, insects, or disease. In contrast, we have focused on identifying genes that, when expressed in soybean, improve the intrinsic ability of the plant to yield more. Through the large scale screening of candidate genes in transgenic soybean, we identified an Arabidopsis thaliana B-box domain gene (AtBBX32) that significantly increases soybean grain yield year after year in multiple transgenic events in multi-location field trials. In order to understand the underlying physiological changes that are associated with increased yield in transgenic soybean, we examined phenotypic differences in two AtBBX32-expressing lines and found increases in plant height and node, flower, pod, and seed number. We propose that these phenotypic changes are likely the result of changes in the timing of reproductive development in transgenic soybean that lead to the increased duration of the pod and seed development period. Consistent with the role of BBX32 in A. thaliana in regulating light signaling, we show that the constitutive expression of AtBBX32 in soybean alters the abundance of a subset of gene transcripts in the early morning hours. In particular, AtBBX32 alters transcript levels of the soybean clock genes GmTOC1 and LHY-CCA1-like2 (GmLCL2). We propose that through the expression of AtBBX32 and modulation of the abundance of circadian clock genes during the transition from dark to light, the timing of critical phases of reproductive development are altered. These findings demonstrate a specific role for AtBBX32 in modulating soybean development, and demonstrate the validity of expressing single genes in crops to deliver increased agricultural productivity.

No abstract

Utilization of native insect resistance genes can be an important component for managing insects in soybean [Glycine max (L.) Merr.]. A major quantitative trait locus (QTL-M) for insect resistance from PI 229358, controlling antibiosis and antixenosis, was previously identified on linkage group (LG) M and was found to increase the effectiveness of a Bacillus thuringiensis (Bt) transgene in soybean. The objectives of this study were to fine-map QTL-M using recombinant substitution lines (RSLs) identified from a 'Benning' backcross population, and to evaluate the main effects and the epistatic interactions between QTL-M and other resistance QTLs on LGs G and H using near-isogenic lines (NILs) in a Benning genetic background. The effect of QTL-M was still detectable in the Benning NILs when they were evaluated for resistance to corn earworm [CEW, Helicoverpa zea (Boddie)]. The two minor resistance QTLs only provided insect resistance when QTL-M was also present in the Benning NILs. The QTL-M was fine-mapped to an approximately 0.52-cM region after the first round of phenotyping the RSLs for resistance to CEW and soybean looper [SBL, Pseudoplusia includens (Walker)]. These results should increase the feasibility of cloning QTL-M and help guide the development of insect resistant soybean cultivars.