Gene interaction at seed-awning loci in the genetic background of wild rice

Abstract

Seed awning is one of the important traits for successful propagation in wild rice. During the domestication of rice by ancient humans, plants with awnless seeds may have been selected because long awns hindered collection and handling activities. To investigate domestication of awnless rice, QTL analysis for seed awning was first carried out using backcross recombinant inbred lines between Oryza sativa Nipponbare (recurrent parent) and O. rufipogon W630 (donor parent). Two strong QTLs were detected in the same regions as known major seed-awning loci, An-1 and RAE2. Subsequent causal mutation surveying and fine mapping confirmed that O. rufipogon W630 has functional alleles at both loci. The gene effects and interactions at these loci were examined using two backcross populations with reciprocal genetic backgrounds of O. sativa Nipponbare and O. rufipogon W630. As awn length in wild rice varied among seeds even in the same plant, awn length was measured based on spikelet position. In the genetic background of cultivated rice, the wild alleles at An-1 and RAE2 had awning effects, and plants having both wild homozygous alleles produced awns whose length was about 70% of those of the wild parent. On the other hand, in the genetic background of wild rice, the substitution of cultivated alleles at An-1 and RAE2 contributed little to awn length reduction. These results indicate that the domestication process of awnless seeds was complicated because many genes are involved in awn formation in wild rice.

Awn Reduction and the Domestication of Asian Rice: A Syndrome or Crop Improvement Trait?

“…Magwa et al 2016: 641, table 1) for a comparison between two Chinese regions, Hainan and Wuhan). iv) Within the same wild as well as domesticated species, the awn length is variable between primary and secondary branches or tillers, and among the five uppermost spikelets on the top primary branch in the panicles (Ikemoto et al 2017;Ishii and Ishikawa 2018).…”

“…Thus it can be correctly said that awn length in rice denotes a phenotypic continuum where length varies from absent or very short (<5 mm; see table 1) to as long as 76.4 mm in Gaoyangdiandahongmang, a japonica variety (Ikemoto et al 2017;Magwa et al 2016), a range almost overlaps with that of wild rice which can harbor both short and long awns (Deb et al 2005;Ikemoto et al 2017: Table 2).…”

“…When present, awns can vary in their rate of development, length, diameter and bristle length. They may be very long (>40 mm), long (>20 mm), short (>5 to ≤ 20 mm) or very short (<5 mm) (Deb et al 2005;Ikemoto et al 2017). They may be straight or curved, single or multiple per floret, barbed or barbless.…”

“…which are awnless). For instance, according toIkemoto et al (2017), the awns are barbed and their length is between 50 to 90 mm in (the wild) O. rufipogon W360, while barbless awns are less than 10 mm in (the domesticated) O. sativa Nipponbare.ii) Within wild species, as well as within domesticated species; even though most wild species have long awns, there are few exceptions, such as Oryza meyeriana, O. schlechteri and O. granulata, which are awnless(Fuller et al 2007). Similarly, while most domesticated landraces are awnless or have only short awns, some are awned, including long (> 20 mm) and very long (> 40 mm) awns, e.g., in an aus strain, Kasalath (15 to 40 mm)(Toriba and Hirano 2014).…”

Identification of Quantitative Trait Loci Controlling Floral Morphology of Rice Using a Backcross Population between Common Cultivated Rice, &lt;i&gt;Oryza sativa&lt;/i&gt; and Asian Wild Rice, &lt;i&gt;O. rufipogon&lt;/i&gt;

“…Lemma has a long hair-like structure called awn that enhances seed shattering in wild rice, but awns are largely absent in cultivated rice [6]. Inside the spikelet, there are six stamens positioned in a whorl and one pistil in the centre.…”