In grass inflorescences, a structure called the "pulvinus" is found between the inflorescence main stem and lateral branches. The size of the pulvinus affects the angle of the lateral branches that emerge from the main axis and therefore has a large impact on inflorescence architecture. Through EMS mutagenesis we have identified three complementation groups of recessive mutants in maize having defects in pulvinus formation. All mutants showed extremely acute tassel branch angles accompanied by a significant reduction in the size of the pulvinus compared with normal plants. Two of the complementation groups correspond to mutations in the previously identified genes, RAMOSA2 (RA2) and LIGULELESS1 (LG1). Mutants corresponding to a third group were cloned using mapped-based approaches and found to encode a new member of the plant-specific TCP (TEOSINTE BRANCHED1/CYCLOIDEA/ PROLIFERATING CELL NUCLEAR ANTIGEN FACTOR) family of DNAbinding proteins, BRANCH ANGLE DEFECTIVE 1 (BAD1). BAD1 is expressed in the developing pulvinus as well as in other developing tissues, including the tassels and juvenile leaves. Both molecular and genetics studies show that RA2 is upstream of BAD1, whereas LG1 may function in a separate pathway. Our findings demonstrate that BAD1 is a TCP class II gene that functions to promote cell proliferation in a lateral organ, the pulvinus, and influences inflorescence architecture by impacting the angle of lateral branch emergence.lateral branch angle | maize inflorescence | architecture | tassel development M aize produces two types of inflorescences: the male tassel at the apex of the plant and the female ears in the axils of vegetative leaves. The tassel forms directly from the shoot apical meristem (SAM) following the elongation and transition of the SAM into an inflorescence meristem. During development the tassel bears four types of higher-order meristems: branch meristems, spikelet pair meristems, spikelet meristems, and floral meristems.

AGAMOUS-like6 (AGL6) genes encode MIKC-type MADS box transcription factors and are closely related to SEPALLATA and AP1/FUL-like genes. Here, we focus on the molecular evolution and expression of the AGL6-like genes in grasses. We have found that AGL6-like genes are expressed in ovules, lodicules (second whorl floral organs), paleas (putative first whorl floral organs), and floral meristems. Each of these expression domains was acquired at a different time in evolution, indicating that each represents a distinct function of the gene product and that the AGL6-like genes are pleiotropic. Expression in the inner integument of the ovule appears to be an ancient expression pattern corresponding to the expression of the gene in the megasporangium and integument in gymnosperms. Expression in floral meristems appears to have been acquired in the angiosperms and expression in second whorl organs in monocots. Early in grass evolution, AGL6-like orthologs acquired a new expression domain in the palea. Stamen expression is variable. Most grasses have a single AGL6-like gene (orthologous to the rice [Oryza sativa] gene MADS6). However, rice and other species of Oryza have a second copy (orthologous to rice MADS17) that appears to be the result of an ancient duplication.

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Inflorescence development in Panicum maximum and Urochloa plantaginea was comparatively studied with scanning electron and light microscopy to test the transfer of P. maximum to Urochloa and to look for developmental features applicable to future cladistic studies of the phosphoenol pyruvate carboxykinase (PCK) subtype of C(4) photosynthesis clade (P. maximum and some species of Brachiaria, Chaetium, Eriochloa, Melinis, and Urochloa). Eleven developmental features not discernable in the mature inflorescence were found: direction of branch differentiation; origins of primary branches; apical vs. intercalary development of the main axis; direction of spikelet differentiation; direction of glume, lemma and palea differentiation; position of the lower glume (in some cases); size of the floret meristem; pattern of distal floret development; pattern of gynoecium abortion; differential pollen development between proximal and distal floret; and glume elongation. Inflorescence homologies between P. maximum and U. plantaginea are also clarified. Panicum maximum and U. plantaginea differ not only in their mature inflorescence structure but also in eight fundamental developmental features that exclude P. maximum from Urochloa. The following developmental events are related to sex expression: size of floret meristem, gynoecium abortion, pollen development delay in the proximal floret, glume elongation and basipetal floret maturation at anthesis.

TCP proteins are plant transcription factors that contain the TCP domain, a conserved domain involved in DNA binding and dimerization (1). The N-terminal portion of the TCP domain is enriched in basic amino acids and is followed by a region that is predicted to contain two amphipathic ␣-helices connected by a disordered loop (2). These features give the TCP domain a resemblance with the bHLH 5 domain present in eukaryotic transcription factors. The basic region, however, differentiates these two structures because this region is longer and contains helix-breaking amino acids in the TCP domain. This makes theoretical predictions about the nature of its contacts with DNA rather inaccurate when bHLH domain-DNA complex structures are used as templates.A broad separation of TCP domains can be made based on amino acid similarities. This produces two main classes of TCP domains that also differ in the number of residues of the basic region because class II proteins contain a 4-amino acid insertion in this region (1, 2). The function of most TCP proteins studied to date is associated with the regulation of different developmental processes in plants (3-11). However, other functions have also been proposed, such as the coordination of mitochondrial biogenesis (12-14), regulation of the circadian clock (15), control of jasmonic acid biosynthesis (16), and determination of the embryonic growth potential in seeds (17). The fact that there are Ͼ20 different TCP proteins in most angiosperm species raises the question of whether there is a high degree of redundancy or different proteins perform different functions and, if the latter case is correct, the additional question is what is the basis for specificity. Studies using mutants and plants overexpressing native or modified forms of TCP proteins have suggested that partial redundancy overlaps with specific functions of different TCP proteins (8,9,16,18).One of the sources of functional specificity may be the existence of different DNA binding preferences among TCP proteins. Previous studies have provided consensus DNA sequences preferentially bound by different class I and class II proteins that, with the sole exception of Arabidopsis TCP11, can be described as GTGGGNCC for class I and GTGGNCCC for class II (11,16,19). Because these kinds of study have only been performed with a limited number of proteins, it is not known whether these consensus sequences apply to all members of each class or not.Studies on the molecular basis of DNA binding specificity of TCP proteins will help to understand how different TCP proteins perform their function and eventually construct a code linking the presence of certain residues to the DNA binding preferences of the respective proteins. In this work, we have studied the DNA binding properties of the class I TCP protein TCP16 from Arabidopsis and determined that it has a preference for a class II binding site. We show that the identity of residue 11 of the class I TCP domain and the equivalent residue 15 of the class II domain is an importan...

Plant transition to land required several regulatory adaptations. The mechanisms behind these changes remain unknown. Since the evolution of transcription factors (TFs) families accompanied this transition, we studied the HOMEODOMAIN LEUCINE ZIPPER (HDZ) TF family known to control key developmental and environmental responses. We performed a phylogenetic and bioinformatics analysis of HDZ genes using transcriptomic and genomic datasets from a wide range of Viridiplantae species. We found evidence for the existence of HDZ genes in chlorophytes and early-divergent charophytes identifying several HDZ members belonging to the four known classes (I-IV). Furthermore, we inferred a progressive incorporation of auxiliary motifs. Interestingly, most of the structural features were already present in ancient lineages. Our phylogenetic analysis inferred that the origin of classes I, III, and IV is monophyletic in land plants in respect to charophytes. However, class IIHDZ genes have two conserved lineages in charophytes and mosses that differ in the CPSCE motif. Our results indicate that the HDZ family was already present in green algae. Later, the HDZ family expanded accompanying critical plant traits. Once on land, the HDZ family experienced multiple duplication events that promoted fundamental neo- and subfunctionalizations for terrestrial life.

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In grasses, inflorescence diversification and its correlation with species evolution are intriguing and not well understood. Part of this problem lies in our lack of comprehension about the inflorescence morphological complexity of grasses. We focused our study on the PCK clade (named for phosphoenol pyruvate carboxykinase), a well-supported monophyletic group for which the relationships among its taxa are not well resolved. Interestingly, the PCK clade has an extensive diversity of adult inflorescence forms. A comparative developmental approach can help us to understand the basis of such morphological differences as well as provide characters that can be used in phylogenetic studies of the group. Using SEM studies, we demonstrate that inflorescence morphology in this clade is even more complex than what is typically observed in adult forms. We describe a number of new characters, and some classical features previously used for taxonomic purposes are redefined on the basis of development. We also define four morphological groups combining adult inflorescence form and development, and we discuss some of the evolutionary aspects of inflorescence diversification in the PCK clade. Taxonomic delimitation among genera in the PCK clade remains confusing and unclear where molecular and morphological studies support different classifications.