Molecular basis of grass inflorescence evolution

REINHEIMER RENATA; JINSHUN ZHONG; ELIZABETH A. KELLOGG

Congreso; XVIII International Botanical Congress; 2011

The grass (Poaceae) family includes about 12000 speciesand over 700 genera segregated into 13 subfamilies.Grasses are widespread all over the world and theireconomic importance is undisputable. Some of thefamily's most well known members are sugar cane,numerous cereal crops such as maize, rice, oat, wheat,etc., and various forage grasses. Grasses are mainlydifferentiated from the rest of the Angiosperms by theirunique flower and inflorescence morphology. Indeed,grass flowers (or florets) do not have conventional sepalsand petals, and instead have two to three fleshy organsnamed lodicules in place of petals, and two empty bracts,presumably known as lemma and palea. One to fortyflorets, depending on the species, are grouped in novelstructures called spikelets, which in turn are located indiverse inflorescence branch systems. The familyexhibits remarkable variation in inflorescencemorphology. Inflorescences may be lax to condensed,spiral, bilateral, or unilateral, with or without a terminalspikelet, with one to many branches varying in the degreeof ramification, length of branch internodes, anddisposition, among other traits. Inflorescence diversity ingrasses is thought to be caused by modifications of thegene regulation that controls their development.Genomes and gene duplications, as well as gene loss, arecommon events in grasses. Duplicated genes can bemaintained in the genome for long periods of timemainly by redundancy (maintenance of the ancestralcopy by the copies), subfunctionalization (splitting up ofthe ancestral role by the copies) or neofunctionalizationprocesses (one of the copies acquires a novel role). Giventhat, variation in when, and where gene copies aretranscribed, and how their protein interacts during organinitiation, and development is thought to be the keyfactor in generating novel forms in grasses. Here we willreport advances in the study of genes that play animportant role in determining inflorescence diversity ingrasses throughout their molecular evolution andmodification of their expression patterns over the courseof grass family evolution.