EVOLUTION OF EMBRYO DORMANCY INVOLVED LOCAL GENE DUPLICATION, RECOMBINATION HOTSPOT FORMATION, AND ADAPTATION TO CHANGING SEED DEVELOPMENT TEMPERATURES IN ORYZA
Gu, X.-Y. and Feng, J.
Agronomy, Horticulture, and Plant Science Department, South Dakota State University, Brookings, USA
Contact: Xing-You Gu, Xingyou.firstname.lastname@example.org
Seed dormancy (SD), a key adaptive trait of both ecological and agricultural importance, can be imposed by physiological/development-related factors in the embryo (embryo dormancy), or enforced by the embryo-surrounding tissues. Natural differentiation of SD between conspecific weedy and cultivated rice (Oryza sativa L.) was associated with quantitative trait loci (QTL).
Some of the QTL alleles isolated from a tropic ecotype of weedy rice are related to specific dormancy types, such as qSD12 for embryo dormancy. qSD12 is the largest QTL, regarding to the size of main effect on germinability reported for cultivated, weedy and wild rice (O. spp.). This major QTL also interacted with other SD loci and with environmental factors (G-by-E) to influence the degree of primary dormancy. qSD12 was further dissected into three physically tightly linked loci (SD12a, b & c), with each having an independent effect and two or three together having cumulative effects on the duration of SD. SD12a and c are annotated as closely related bHLH family transcription factors, while SD12b encodes a protein of unknown molecular function. The SD12s (SD12a, b & c) were highly expressed in 10-d embryos and influenced transcriptional levels of heat shock protein and other stress-responsive genes. SD12a and c were involved in G-by-E interactions, resulting in enhanced dormancy in relatively high temperature environments during seed development. Both SD12a and c have a local duplicate flanked or separated by tandem repeats of transposable elements, but these bHLH duplicates had no phenotypic effect. This multigenic QTL region is equipped with two recombination hotspots, which increased recombination fractions between SD12s and between SD12s and their flanking regions. Corresponding to the presence of recombination hotspots, the haplotype for functional alleles at all SD12s is present only in some tropical ecotypes of wild or weedy rice from Southern Thailand. This research advanced our understanding on the origin, genome organization and functional differentiation of natural genes controlling embryo dormancy, and provided novel genes to manipulate germinability in crop breeding.
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