Genome-wide Expression Pattern Analyses Of LRR-RLKs And Study Of ELE Regulating Plastochron Length Of Leaf In Arabidopsis

Receptor-like protein kinases(RLKs) are a large group of transmembrane proteins playing critical roles in cell-cell and cell-environment communications. Based on extracellular domain structures, RLKs were classified into more than 21 subfamilies, among which leucine-rich repeat RLKs(LRR-RLKs) belong to the largest subfamily in plants such as Arabidopsis and rice. In Arabidopsis, there are approximately 223 LRR-RLKs. Only about 60 of them have been functionally described. The majority of them need to be functionally determined. To systematically investigate their roles in regulating plant growth, development and stress adaptations, we generated promoter::GUS transgenic plants for all 223 LRR-RLKs and analyzed their detailed expression patterns in tissues and organs at various developmental stages, such as seedlings, roots and lateral roots, cotyledons, rosette leaves and its specialized structures(guard cells and trichomes) in vegetative stage and inflorescences, mature flowers and mature siliques in reproductive stage. These results provide valuable resources for the research community to functionally elucidate this large and essential signaling protein subfamily.Leaf number, as a major factor of biomass in vegetative growth stage, is essential for agricultural production, which makes it especially important to understand the leaf growth and development and the rate of leaf growth. However, studies at the genetic and molecular level on the rate of leaf production or plastochron are largely unknown. A mutant affecting leaf numbers of Arabidopsis was obtained by activation tagging in a previous screen in the background of bri1-5. The flanking sequences of the T-DNA insertion site were isolated by TAIL-PCR and the corresponding gene was identified. The loss-of-function mutant of the gene produced more rosette leaves than wild type plants without affecting the flowering time, and therefore the gene was named as EXTRA LEAF(ELE). Comparative genomics analysis by online tool PLAZA3.0 found that ELE is an atypical and dicot-specific protein kinase gene in higher plants. The loss-of-function mutant ele-1 exhibits phenotypes of accelerated growth and development of rosette leaves. Results of in situ hybridization and expression pattern analysis of GUS reporter gene showed that ELE is specifically expressed in leaf primordia and early young leaves. ELE affects not only the number of rosette leaves, but also the phyllotaxy to some extent. To further investigate the function of ELE, RNAseq analysis was performed to analyze the differential expressed genes(DEGs) between the mutant and wide type plants just before they displayed any phenotypic differences. The results showed that the transcript levels of CYP78A5/KLU, a plastochron-related gene, are significantly reduced, and mRNA levels of some expansin genes are increased in the mutant ele-1. Double mutant ele-1 cyp78a5 shows the same level of leaf growth as cyp78a5, but both of them have higher rate than ele-1, indicating that CYP78A5 may function downstream of ELE to regulate the rate of leaf production or plastochron.