Friday, January 12, 2007

News: Seed shattering selection in rice domestication

Haven't read the article yet, but the abstract below makes some
interestng claims.

If I read it right, it suggests that artificial selection for rice
plants that do not shatter seeds, began before the differentiation of
indica and japonica.

This suggests rather strongly, since the specific single mutation is
identified, and contrary to some other recent studies, that both
indica and japonica descend from a single *domesticated* ancestor.

Paul Kekai Manansala

Planta. 2007 Jan 10;
Origin of seed shattering in rice (Oryza sativa L.).

* Lin Z,
* Griffith ME,
* Li X,
* Zhu Z,
* Tan L,
* Fu Y,
* Zhang W,
* Wang X,
* Xie D,
* Sun C.

Department of Plant Genetics and Breeding and State Key Laboratory
of Agrobiotechnology, China Agricultural University, Key Laboratory of
Crop Heterosis and Utilization of Ministry of Education, Beijing Key
Laboratory of Crop Genetic Improvement, Key Laboratory of Crop Genetic
Improvement and Genome of Ministry of Agriculture, Beijing, 100094,
China, suncq@....

A critical evolutionary step during rice domestication was the
elimination of seed shattering. Wild rice disperses seeds freely at
maturity to guarantee the propagation, while cultivated rice retains
seeds on the straws to make easy harvest and decrease the loss of
production. The molecular basis for this key event during rice
domestication remains to be elucidated. Here we show that the seed
shattering is controlled by a single dominant gene, Shattering1
(SHA1), encoding a member of the trihelix family of plant-specific
transcription factors. SHA1 was mapped to a 5.5 kb genomic fragment,
which contains a single open reading frame, using a backcrossed
population between cultivated rice Teqing and an introgression line
IL105 with the seed shattering habit derived from perennial common
wild rice, YJCWR. The predicted amino acid sequence of SHA1 in YJCWR
and IL105 is distinguished from that in eight domesticated rice
cultivars, including Teqing, by only a single amino acid substitution
(K79N) caused by a single nucleotide change (g237t). Further sequence
verification on the g237t mutation site revealed that the g237t
mutation is present in all the domesticated rice cultivars, including
92 indica and 108 japonica cultivars, but not in any of the 24 wild
rice accessions examined. Our results demonstrate that the g237t
mutation in SHA1 accounts for the elimination of seed shattering, and
that all the domesticated rice cultivars harbor the mutant sha1 gene
and therefore have lost the ability to shed their seeds at maturity.
In addition, our data support the theory that the non-shattering trait
selection during rice domestication occurred prior to the
indica-japonica differentiation in rice evolutionary history.