The domestication of cereal crops such as wheat, maize, rice and barley has included the modification of inflorescence architecture to improve grain yield and ease harvesting(1). Yield increases have often been achieved through modifying the number and arrangement of spikelets, which are specialized reproductive branches that form part of the inflorescence. Multiple genes that control spikelet development have been identified in maize, rice and barley(2-5). However, little is known about the genetic underpinnings of this process in wheat. Here, we describe a modified spikelet arrangement in wheat, termed paired spikelets. Combining comprehensive QTL and mutant analyses, we show that Photoperiod-1 (Ppd-1), a pseudo-response regulator gene that controls photoperiod-dependent floral induction, has a major inhibitory effect on paired spikelet formation by regulating the expression of FLOWERING LOCUS T (FT)(6,7). These findings show that modulated expression of the two important flowering genes, Ppd-1 and FT, can be used to form a wheat inflorescence with a more elaborate arrangement and increased number of grain producing spikelets.

The flowers of major cereals are arranged on reproductive branches known as spikelets, which group together to form an inflorescence. Diversity for inflorescence architecture has been exploited during domestication to increase crop yields, and genetic variation for this trait has potential to further boost grain production. Multiple genes that regulate inflorescence architecture have been identified by studying alleles that modify gene activity or dosage; however, little is known in wheat. Here, we show () regulates inflorescence architecture in bread wheat () by investigating lines that display a form of inflorescence branching known as "paired spikelets." We show that TB1 interacts with FLOWERING LOCUS T1 and that increased dosage of alters inflorescence architecture and growth rate in a process that includes reduced expression of meristem identity genes, with allelic diversity for found to associate genetically with paired spikelet development in modern cultivars. We propose coordinates formation of axillary spikelets during the vegetative to floral transition and that alleles known to modify dosage or function of could help increase wheat yields.

Using a two-element iAc/Ds transposon-tagging system, we identified a rice (Oryza sativa L. cv Nipponbare) recessive mutant, anther indehiscence1 (aid1), showing partial to complete spikelet sterility. Spikelets of the aid1 mutant could be classified into three types based on the viability of pollen grains and the extent of anther dehiscence. Type 1 spikelets (approximately 25%) were sterile due to a failure in accumulation of starch in pollen grains. Type 2 spikelets (approximately 55%) had viable pollen grains, but anthers failed to dehisce and/or synchronize with anthesis due to failure in septum degradation and stomium breakage, resulting in sterility. Type 3 spikelets (approximately 20%) had normal fertility. In addition, aid1 mutant plants had fewer tillers and flowered 10 to 15 d later than the wild type. The Ds insertion responsible for the aid1 mutation was mapped within the coding region of the AID1 gene on chromosome 6, which is predicted to encode a novel protein of 426 amino acids with a single MYB domain. The MYB domain of AID1 is closely related to that of the telomere-binding proteins of human, mouse, and Arabidopsis, and of single MYB domain transcriptional regulators in plants such as PcMYB1 and ZmIBP1. AID1 was expressed in both the leaves and panicles of wild-type plants, but not in mutant plants.Anther dehiscence is the final step of anther development and results in the release of pollen grains to enable pollination, fertilization, and seed set (Goldberg et al., 1993). In anthers, three tissues-endothecium, septum, and stomium-play important roles in anther dehiscence. The endothecium is an anther wall tissue lying between the epidermal layer and the tapetum. The septum is a filling tissue for spaces between vascular bundles and the two adjacent anther locules. The stomium is a single layer of specialized epidermal cells that joins adjacent anther walls and is the final breakage site for anther dehiscence (Keijzer, 1987). In rice (Oryza sativa), at the beginning of anthesis, filaments begin to elongate and pollen grains swell rapidly. The increased pollen pressure causes the locule to bulge, resulting in rupture of the septum that has been weakened by hydrolytic enzyme action. Subsequent lysis of the middle lamellae of the stomium cells, pollen pressure, and the force induced by the inward bending of the locules causes the stomium to split (Keijzer et al., 1996;Matsui et al., 1999). Finally, shrinkage of the U-shaped, thickened endothecium induces the outward bending of locules, which widens the theca to release swollen pollen grains. Meanwhile, for successful anther dehiscence and pollination, a series of developmental events that leads to the breakage of the stomium and release of pollen grains must synchronize with other developmental processes that occur within both the anther and the floret. However, little is know about the mechanisms that control and coordinate many of these developmental events. Identification of mutants defective in any of these developmental activities would shed ...