Jing Liu , Wei Hua , Zhiyong Hu , Hongli Yang , Liang Zhang , Rongjun Li , Linbin Deng , Xingchao Sun , Xinfa Wang and Hanzhong Wang

Agricultural Sciences

Significance

Seed weight is a complex trait controlled by polygenes, and its underlying regulatory mechanisms, especially those involving polyploidy crops, remain elusive. Brassica napus L., which is the second leading crop source of vegetable oil around the world, is an important tetraploid (4×) crop. Our results have generated three significant findings. (i) By combining the linkage and associated analysis, this study revealed the first (to our knowledge) quantitative trait locus (QTL) in rapeseed, which will provide insights for QTL cloning in polyploidy crops. (ii) The functional gene and marker could be useful in rapeseed breeding. (iii) We revealed a maternal regulatory pathway affecting seed weight that differs from the mechanisms described in previous reports.

Abstract

Seed weight (SW), which is one of the three major factors influencing grain yield, has been widely accepted as a complex trait that is controlled by polygenes, particularly in polyploid crops. Brassica napus L., which is the second leading crop source for vegetable oil around the world, is a tetraploid (4×) species. In the present study, we identified a major quantitative trait locus (QTL) on chromosome A9 of rapeseed in which the genes for SW and silique length (SL) were colocated. By fine mapping and association analysis, we uncovered a 165-bp deletion in the auxin-response factor 18 (ARF18) gene associated with increased SW and SL. ARF18 encodes an auxin-response factor and shows inhibitory activity on downstream auxin genes. This 55-aa deletion prevents ARF18 from forming homodimers, in turn resulting in the loss of binding activity. Furthermore, reciprocal crossing has shown that this QTL affects SW by maternal effects. Transcription analysis has shown that ARF18 regulates cell growth in the silique wall by acting via an auxin-response pathway. Together, our results suggest that ARF18 regulates silique wall development and determines SW via maternal regulation. In addition, our study reveals the first (to our knowledge) QTL in rapeseed and may provide insights into gene cloning involving polyploid crops.

See: http://www.pnas.org/content/112/37/E5123.abstract.html?etoc

PNAS September 15 2015, vol. 112 no. 37: E5123–E5132