‡SUMMARY Gibberellins (GA) are an important family of plant growth regulators, which are essential for many aspects of plant growth and development. In the GA signaling pathway, the action of GA is opposed by a group of DELLA family repressors, such as RGA. Although the mechanisms of action of the DELLA proteins have been studied in great detail, the effectors that act downstream of DELLA proteins and bring about GA-responsive growth and development remain largely unknown. In this study, we have characterized STUNTED (STU), a receptor-like cytoplasmic kinase (RLCK) VI family gene, which is ubiquitously detectable in all the tissues examined. RGA activity and GA signaling specifically mediate the levels of STU transcripts in shoot apices that contain actively dividing cells. stu-1 loss-of-function mutants exhibit retarded growth in many aspects of plant development. During the vegetative phase, stu-1 seedlings develop smaller leaves and shorter roots than wild-type seedlings, while during the reproductive phase, stu-1 exhibits delayed floral transition and lower fertility. The reduced stature of stu-1 partly results from a reduction in cell proliferation. Furthermore, we present evidence that STU serves as an important regulator mediating the control of cell proliferation by GA possibly through two cyclin-dependent kinase inhibitors, SIM and SMR1. Taken together, our results suggest that STU acts downstream of RGA and promotes cell proliferation in the GA pathway.
Salinity affects crop productivity worldwide and mangroves growing under high salinity exhibit adaptations such as enhanced root apoplastic barrier to survive under such conditions. We have identified two cytochrome P450 family genes, AoCYP94B3 and AoCYP86B1 from the mangrove tree Avicennia officinalis and characterized them using atcyp94b3 and atcyp86b1, which are mutants of their putative Arabidopsis orthologs and the corresponding complemented lines with A. officinalis genes. CYP94B3 and CYP86B1 transcripts were induced upon salt treatment in the roots of both A. officinalis and Arabidopsis. Both AoCYP94B3 and AoCYP86B1 were localized to the endoplasmic reticulum. Heterologous expression of 35S::AoCYP94B3 and 35S::AoCYP86B1 in their respective Arabidopsis mutants (atcyp94b3 and atcyp86b1) increased the salt tolerance of the transgenic seedlings by reducing the amount of Na+ accumulation in the shoots. Moreover, the reduced root suberin phenotype of atcyp94b3 was rescued in the 35S::AoCYP94B3;atcyp94b3 transgenic Arabidopsis seedlings. Gas-chromatography and mass spectrometry analyses showed that the amount of suberin monomers (C-16 ω-hydroxy acids, C-16 α, ω-dicarboxylic acids and C-20 eicosanol) were increased in the roots of 35S::AoCYP94B3;atcyp94b3 Arabidopsis seedlings. Using chromatin immunoprecipitation and electrophoretic mobility shift assays, we identified AtWRKY9 as the upstream regulator of AtCYP94B3 and AtCYP86B1 in Arabidopsis. In addition, atwrky9 showed suppressed expression of AtCYP94B3 and AtCYP86B1 transcripts, and reduced suberin in the roots. These results show that AtWRKY9 controls suberin deposition by regulating AtCYP94B3 and AtCYP86B1, leading to salt tolerance. Our data can be used for generating salt-tolerant crop plants in the future.
Abstract Aim Biogeographical barriers restrict the movement of individuals, resulting in population divergence, genetic differentiation, endemism and speciation. Yet, some barriers demonstrate unequal effect across species depending on species dispersal, which manifests in varying genetic structure. We test the hypotheses that the genetic structure of four coastal mangrove species would reflect differences in dispersal potential across the Malay Peninsula, a major biogeographical barrier in the Indo‐West Pacific region. Location East and west coasts of the Malay Peninsula. Taxon Mangrove trees Avicennia alba , Sonneratia alba , Bruguiera gymnorhiza and Rhizophora mucronata. Methods For each species, we characterized genetic structure and gene flow using 7–12 species‐specific nuclear microsatellite markers. We tested for east–west genetic differentiation across the peninsula, a stepping‐stone migration pattern, and assessed the proportion of recent dispersal and direction of historical migration along the Malacca Strait. Results Significant east–west genetic differentiation across the peninsula was observed in A. alba , S. alba and B. gymnorhiza , and the effect was most pronounced for the two species with lower dispersal potential ( A. alba , S. alba ). In contrast, the two species with higher dispersal potential ( B. gymnorhiza and R. mucronata ) exhibited much higher proportion of recent inter‐population migration along the Malacca Strait. The signature of historical colonization from refugia in the Andaman Sea (north‐to‐south migration along the Malacca Strait) predominated for A. alba and S. alba. Historical south–north migration predominated for R. mucronata and B. gymnorhiza . Main conclusions This study implicated dispersal potential as a cause of varying mangrove species genetic structure across a biogeographical barrier. The Malay Peninsula functions as a filter to gene flow rather than a barrier. The genetic structure in mangrove species with a higher dispersal potential is more congruent with contemporary gene flow while that of species with a lower dispersal potential reflects historical processes. Our findings hint at the role of dispersal potential as a predictor of gene flow in mangroves.
Many Heliconia species are polymorphic with a large number of cultivars. Cultivar identification has been primarily based on morphological differences of the flowers and inflorescences. A protocol was developed to extract DNA from Heliconia leaves and to analyze genetic variation using RAPD. The percentage genetic similarities among Heliconia species, cultivars, and hybrids were determined. Data from 11 primers indicated that the RAPD technique is useful in distinguishing species and cultivars of Heliconia. Using a single 10-mer primer (OPA 18), we were able to generate distinct RAPD profiles for 16 cultivars of H. psittacorum L.f. grown at the Jurong BirdPark, Singapore, a Heliconia Society International depository. Hence, the characteristic profiles generated by RAPD may be used as additional DNA markers for classifying different species and cultivars of Heliconia. The phylogenetic tree derived from the RAPD data showed that all the 16 cultivars examined are closely related to each other, thus providing the first genetic evidence that this large group of cultivars has a common genetic background. Moreover, two triploid cultivars of H. psittacorum —`Iris' and `Petra'—showed identical RAPD profiles with 10 different primers in agarose and polyacrylamide gels, suggesting that they are of the same genotype.
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