Overexpression of AtAHL20 causes delayed flowering in Arabidopsis via repression of FT expression

The 29-member Arabidopsis AHL gene family is classified into three main classes based on nucleotide and protein sequence evolutionary differences. These differences include the presence or absence of introns, type and/or number of conserved AT-hook and PPC domains. AHL gene family members are divided into two phylogenetic clades, Clade-A and Clade-B. A majority of the 29 members remain functionally uncharacterized. Furthermore, the biological significance of the DNA and peptide sequence diversity, observed in the conserved motifs and domains found in the different AHL types, is a subject area that remains largely unexplored. Transgenic plants overexpressing AtAHL20 flowered later than the wild type under both short and long days. Transcript accumulation analyses showed that 35S:AtAHL20 plants contained reduced FT, TSF, AGL8 and SPL3 mRNA levels. Similarly, overexpression of AtAHL20’s orthologue in Camelina sativa, Arabidopsis’ closely related Brassicaceae family member species, conferred a late-flowering phenotype via suppression of CsFT expression. However, overexpression of an aberrant AtAHL20 gene harboring a missense mutation in the AT-hook domain’s highly conserved R-G-R core motif abolished the late-flowering phenotype. Data from targeted yeast-two-hybrid assays showed that AtAHL20 interacted with itself and several other Clade-A Type-I AHLs which have been previously implicated in flowering-time regulation: AtAHL19, AtAHL22 and AtAHL29. We showed via gain-of-function analysis that AtAHL20 is a negative regulator of FT expression, as well as other downstream flowering time regulating genes. A similar outcome in Camelina sativa transgenic plants overexpressing CsAHL20 suggest that this is a conserved function. Our results demonstrate that AtAHL20 acts as a photoperiod-independent negative regulator of transition to flowering.https://doi.org/10.1186/s12870-020-02733-

Auxin regulates adventitious root formation in tomato cuttings

Adventitious root (AR) formation is a critical developmental process in cutting propagation for the horticultural industry. While auxin has been shown to regulate this process, the exact mechanism and details preceding AR formation remain unclear. Even though AR and lateral root (LR) formation share common developmental processes, there are exist some differences that need to be closely examined at the cytological level. Tomato stem cuttings, which readily form adventitious roots, represent the perfect system to study the influence of auxin on AR formation and to compare AR and LR organogenesis.https://doi.org/10.1186/s12870-019-2002-

Molecular genetic analysis of two plant-specific gene families, SOFL and AHL, in Arabidopsis thaliana

SOFL (SOB FIVE-LIKE) and AHL (AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED) are plant specific gene families in Arabidopsis. This study focuses on characterizing gene members in both families using over-expression analysis.There are 29 AHLs in Arabidopsis but only eleven have been characterized at the molecular and genetic level. This study focused on two AHL members, AtAHL6 and AtAHL20, which belong to two different phylogenetic clades. Histochemical analysis of plants harboring proAtAHL6-GUS and proAtAHL20-GUS transcriptional fusion constructs revealed distinct expression patterns. Plants harboring the proAtAHL6-GUS construct showed GUS signal in root tips of Arabidopsis seedlings but not in rosette leaves and floral structures. ProAtAHL20-GUS seedlings revealed GUS activity in roots, hypocotyls and cotyledons. AtAHL20 was also expressed in rosette leaves and floral structures. Over-expression analysis of wild-type and aberrant versions of AtAHL6 and AtAHL20 proteins revealed that they are involved in regulation of flowering time in an opposite manner. 35S:AtAHL6 transgenic plants flowered earlier than wild-type plants in a photoperiod dependent manner. In contrast, 35S:AtAHL20 transgenic plants exhibited delayed flowering compared to wild-type plants in a photoperiod independent manner. Over-expression of AtAHL6 and AtAHL20 proteins carrying point mutations in a highly conserved motif, the AT-Hook, led to the loss of AtAHL20’s over-expression phenotype but not AtAHL6’s.Gain-of-function and loss-of-function analyses of three founding SOFL family members; SOB5, AtSOFL1 and AtSOFL2, suggested that they are involved in cytokinin-mediated plant development. Database searches led to the retrieval of 195 sequences from dicotyledon and monocotyledon species. Arabidopsis thaliana has 11 SOFL members. Multiple sequence alignment of all SOFLs from 57 species revealed two conserved domains; SOFL-A and SOFL-B. Structure/function analysis using SOB5, AtSOFL1 and AtSOFL2 showed that these domains are important for function. Subcellular localization studies using the founding SOFL members showed that they localize in the nucleus. A sob5-2 sofl1RNAi sofl2-1 triple mutant did not show any additional phenotypes versus wild-type plants, suggesting that there is still functional redundancy among the 11 SOFLs in Arabidopsis thaliana

Genetic Resources for Maize Cell Wall Biology1[C][W][OA]

Grass species represent a major source of food, feed, and fiber crops and potential feedstocks for biofuel production. Most of the biomass is contributed by cell walls that are distinct in composition from all other flowering plants. Identifying cell wall-related genes and their functions underpins a fundamental understanding of growth and development in these species. Toward this goal, we are building a knowledge base of the maize (Zea mays) genes involved in cell wall biology, their expression profiles, and the phenotypic consequences of mutation. Over 750 maize genes were annotated and assembled into gene families predicted to function in cell wall biogenesis. Comparative genomics of maize, rice (Oryza sativa), and Arabidopsis (Arabidopsis thaliana) sequences reveal differences in gene family structure between grass species and a reference eudicot species. Analysis of transcript profile data for cell wall genes in developing maize ovaries revealed that expression within families differed by up to 100-fold. When transcriptional analyses of developing ovaries before pollination from Arabidopsis, rice, and maize were contrasted, distinct sets of cell wall genes were expressed in grasses. These differences in gene family structure and expression between Arabidopsis and the grasses underscore the requirement for a grass-specific genetic model for functional analyses. A UniformMu population proved to be an important resource in both forward- and reverse-genetics approaches to identify hundreds of mutants in cell wall genes. A forward screen of field-grown lines by near-infrared spectroscopic screen of mature leaves yielded several dozen lines with heritable spectroscopic phenotypes. Pyrolysis-molecular beam mass spectrometry confirmed that several nir mutants had altered carbohydrate-lignin compositions