Taking Hormone Crosstalk to a New Level: Brassinosteroids Regulate Gibberellin Biosynthesis

A Novel Mutation of the NARROW LEAF 1 Gene Adversely Affects Plant Architecture in Rice (Oryza sativa L.)

Plant architecture is critical for enhancing the adaptability and productivity of crop plants. Mutants with an altered plant architecture allow researchers to elucidate the genetic network and the underlying mechanisms. In this study, we characterized a novel nal1 rice mutant with short height, small panicle, and narrow and thick deep green leaves that was identified from a cross between a rice cultivar and a weedy rice accession. Bulked segregant analysis coupled with genome re-sequencing and cosegregation analysis revealed that the overall mutant phenotype was caused by a 1395-bp deletion spanning over the last two exons including the transcriptional end site of the nal1 gene. This deletion resulted in chimeric transcripts involving nal1 and the adjacent gene, which were validated by a reference-guided assembly of transcripts followed by PCR amplification. A comparative transcriptome analysis of the mutant and the wild-type rice revealed 263 differentially expressed genes involved in cell division, cell expansion, photosynthesis, reproduction, and gibberellin (GA) and brassinosteroids (BR) signaling pathways, suggesting the important regulatory role of nal1. Our study indicated that nal1 controls plant architecture through the regulation of genes involved in the photosynthetic apparatus, cell cycle, and GA and BR signaling pathways.

Mediation of Flower Induction by Gibberellin and its Inhibitor Paclobutrazol: mRNA and miRNA Integration Comprises Complex Regulatory Cross-Talk in Apple

Guaranteeing successful flowering is very important in economic plant species, especially apple (Malus domestica Borkh.), which is difficult to induce to flower. However, the gene expression and networks involved in flowering have not been totally characterized. Here, we employed mRNA and microRNA (miRNA) sequencing to understand the different responses to gibberellin- and its inhibitor paclobutrazol- (PAC) mediated flower induction. Significant opposite cytological and morphological changes were observed in treated terminal buds, which led to a reduced flowering rate under gibberellin and an increased flowering rate under PAC. We also found that the differentially expressed mRNAs, miRNAs and miRNA target genes participated in different biological networks including hormones, photosynthesis, redox state and other metabolic processes, which provided important clues to understand the complex networks involved in apple flower induction. Additionally, we subsequently focused on one important candidate, MdSPL3, which is one of 31 apple SPL gene family members and whose transcription was inhibited by gibberellin but promoted by PAC. Functional investigation showed that MdSPL3 was located in the nucleus, and ectopic MdSPL3 activated floral meristem identity genes, promoted the formation of floral primordia and led to an earlier flowering phenotype in Arabidopsis. Our research identified critical mRNA and miRNA responsive to gibberellin or PAC, and provided a candidate framework for flower induction. This carefully orchestrated regulatory cross-talk highlighted potential targets for developing regulatory techniques and genetic improvement of flower induction in apple.

Gibberellins Promote Brassinosteroids Action and Both Increase Heterosis for Plant Height in Maize (Zea mays L.)

Brassinosteroids (BRs) and Gibberellins (GAs) are two classes of plant hormones affecting plant height (PHT). Thus, manipulation of BR and GA levels or signaling enables optimization of crop grain and biomass yields. We established backcross (BC) families, selected for increased PHT, in two elite maize inbred backgrounds. Various exotic accessions used in the germplasm enhancement in maize project served as donors. BC1-derived doubled haploid lines in the same two elite maize inbred backgrounds established without selection for plant height were included for comparison. We conducted genome-wide association studies to explore the genetic control of PHT by BR and GA. In addition, we used BR and GA inhibitors to compare the relationship between PHT, BR, and GA in inbred lines and heterozygotes from a physiological and biological perspective. A total of 73 genomic loci were discovered to be associated with PHT, with seven co-localized with GA, and two co-localized with BR candidate genes. PHT determined in field trials was significantly correlated with seedling stage BR and GA inhibitor responses. However, this observation was only true for maize heterozygotes, not for inbred lines. Path analysis results suggest that heterozygosity increases GA levels, which in turn promote BR levels. Thus, at least part of heterosis for PHT in maize can be explained by increased GA and BR levels, and seedling stage hormone inhibitor response is promising to predict heterosis for PHT.

The potential of the mevalonate pathway for enhanced isoprenoid production

The cytosol-localised mevalonic acid (MVA) pathway delivers the basic isoprene unit isopentenyl diphosphate (IPP). In higher plants, this central metabolic intermediate is also synthesised by the plastid-localised methylerythritol phosphate (MEP) pathway. Both MVA and MEP pathways conspire through exchange of intermediates and regulatory interactions. Products downstream of IPP such as phytosterols, carotenoids, vitamin E, artemisinin, tanshinone and paclitaxel demonstrate antioxidant, cholesterol-reducing, anti-ageing, anticancer, antimalarial, anti-inflammatory and antibacterial activities. Other isoprenoid precursors including isoprene, isoprenol, geraniol, farnesene and farnesol are economically valuable. An update on the MVA pathway and its interaction with the MEP pathway is presented, including the improvement in the production of phytosterols and other isoprenoid derivatives. Such attempts are for instance based on the bioengineering of microbes such as Escherichia coli and Saccharomyces cerevisiae, as well as plants. The function of relevant genes in the MVA pathway that can be utilised in metabolic engineering is reviewed and future perspectives are presented.