APETALA 2‐

The spikelet is the basic unit of the grass inflorescence. In tetraploid (Triticum turgidum) and hexaploid wheat (Triticum aestivum), the spikelet is a short indeterminate branch with two proximal sterile bracts (glumes) followed by a variable number of florets, each including a bract (lemma) with an axillary flower. Varying levels of miR172 and/or its target gene Q (AP2L5) result in gradual transitions of glumes to lemmas, and vice versa. Here, we show that AP2L5 and its related paralog AP2L2 play critical and redundant roles in the specification of axillary floral meristems and lemma identity. AP2L2, also targeted by miR172, displayed similar expression profiles to AP2L5 during spikelet development. Loss-of-function mutants in both homeologs of AP2L2 (henceforth ap2l2) developed normal spikelets, but ap2l2 ap2l5 double mutants generated spikelets with multiple empty bracts before transitioning to florets. The coordinated nature of these changes suggest an early role of these genes in floret development. Moreover, the flowers of ap2l2 ap2l5 mutants showed organ defects in paleas and lodicules, including the homeotic conversion of lodicules into carpels. Mutations in the miR172 target site of AP2L2 were associated with reduced plant height, more compact spikes, promotion of lemma-like characters in glumes and smaller lodicules. Taken together, our results show that the balance in the expression of miR172 and AP2-like genes is crucial for the correct development of spikelets and florets, and that this balance has been altered during the process of wheat and barley (Hordeum vulgare) domestication. The manipulation of this regulatory module provides an opportunity to modify spikelet architecture and improve grain yield

Implementação da seleção recorrente no melhoramento de plantas autógamas através da macho-esterilidade Implementation of recurrent selection in plant breding of autogamous crops through male sterility

Os sistemas de melhoramento convencionais baseados no método genealógico, utilizados principalmente em cereais de estação fria, determinam a redução da variabilidade e da capacidade de recombinação, devido a utilização de um número de genitores limitado nos cruzamentos. O incremento da probabilidade de recombinação através da seleção recorrente pelo aumento do número de cruzamentos pode ser a saída para este problema. A utilização da macho-esterilidade representa uma alternativa viável para propiciar o cruzamento natural em espécies de autofecundação, favorecendo a utilização da seleção recorrente como uma importante ferramenta para o melhoramento de plantas autógamas.<br>The mechanism of pedigree system used in smallgrain cereals reduce genetic variability and recombination capacity due to the limited number of parent used in crosses. The increase in recombination through recurrent selection by maximizing number of crosses may be a solution for this problem. The use of male sterility may overcome the difficult of performing artificial crosses, supporting recurrent selection as a viable and important tool for autogamous crops breeding