Convergent evolution of perenniality in rice and sorghum

Abstract

Annual and perennial habit are two major strategies by which grasses adapt to seasonal environmental change, and these distinguish cultivated cereals from their wild relatives. Rhizomatousness, a key trait contributing to perenniality, was investigated by using an F 2 population from a cross between cultivated rice (Oryza sativa) and its wild relative, Oryza longistaminata. Molecular mapping based on a complete simple sequence-repeat map revealed two dominant-complementary genes controlling rhizomatousness. Rhz3 was mapped to the interval between markers OSR16 [1.3 centimorgans (cM)] and OSR13 (8.1 cM) on rice chromosome 4 and Rhz2 located between RM119 (2.2 cM) and RM273 (7.4 cM) on chromosome 3. Comparative mapping indicated that each gene closely corresponds to major quantitative trait loci (QTLs) controlling rhizomatousness in Sorghum propinquum, a wild relative of cultivated sorghum. Correspondence of these genes in rice and sorghum, which diverged from a common ancestor Ϸ50 million years ago, suggests that the two genes may be key regulators of rhizome development in many Poaceae. Many additional QTLs affecting abundance of rhizomes in O. longistaminata were identified, most of which also corresponded to the locations of S. propinquum QTLs. Convergent evolution of independent mutations at, in some cases, corresponding genes may have been responsible for the evolution of annual cereals from perennial wild grasses. DNA markers closely linked to Rhz2 and Rhz3 will facilitate cloning of the genes, which may contribute significantly to our understanding of grass evolution, advance opportunities to develop perennial cereals, and offer insights into environmentally benign weed-control strategies.

Hormonal Regulation of Branching in Grasses

“…For example, increased planting density reduces tiller number and increased fertilizer treatment increases tiller number. Genetic studies show that perennialism is controlled by relatively few genes (Hu et al, 2003;Westerbergh and Doebley, 2004). The identification of these genes will be essential for understanding the regulation of branching in perennial grasses.…”

The Evolutionary History of Ehrhartoideae, Oryzeae, and Oryza

“…3). In an F 2 mapping population of O. sativa crossed with Oryza longistaminata, Hu et al (2003) have identified multiple QTL that correlate with the presence of rhizomes, which are often correlated with the perennial habit. Two of these loci overlap with similar loci in sorghum suggesting that a few major regulators control growth form in many species of grasses.…”

Evolutionary fate of rhizome-specific genes in a non-rhizomatous Sorghum genotype

“…Recently, Li et al (2006) reported that reduced shattering of the mature inflorescence associated with rice domestication was caused in part by human selection of an amino acid substitution in the DNAbinding domain of the sh4 gene. Rhz2 and Rhz3 might be targets for such macro-mutations affecting rhizomatousness (Hu et al, 2003). However, little is known on the fate of many genes involved in the molecular pathway after the genotype has lost the ability of rhizomatousness.…”

“…The Sorghum genus has become a model for dissecting the molecular control of rhizomatousness (Paterson et al, 1995;Hu et al, 2003;Jang et al, 2006). S. halepense L. Pers.…”