Nam-Hai Chua has made many original contributions to plant cell and developmental biology. He discovered the D2 protein and other chlorophyll–protein complexes related to the photosystem II reaction centre. With others, he demonstrated that the small subunit of RuBisCo is synthesised as a precursor on free cytoplasmic ribosomes and uncovered many of the details of its subsequent transport into the chloroplast. His laboratory demonstrated that the cauliflower mosaic virus 35S promoter can be used to transcribe heterologous coding sequences in transgenic plants. This strong, constitutive promoter has become an important tool in basic plant biology research and is also widely used to express transgenic traits in crops.
His current work on the control of gene expression in transgenic plants is laying the groundwork for new advances in plant breeding. Nam-Hai serves as scientific adviser to companies and government-related organizations in several countries.
Professor Chua is the Andrew W. Mellon Professor (Emeritus) at The Rockefeller University, a Temasek Senior Investigator (Emeritus), Temasek Life Sciences Laboratory (TLL), and a Distinguished Visiting Professor, Biochemistry Department, National University of Singapore. Also a Fellow of the UK Royal Society, an Academician of Taiwan’s Academia Sinica, and a Foreign Academician of the Chinese Academy of Sciences, China, Professor Chua has advised government organisations, institutions and MNCs worldwide, including Monsanto, DUPONT, Sumitomo Chemical Corporation, and biotechnology-related entities. He received his B.Sc. from University of Singapore; A.M. and Ph.D from Harvard University; and an honorary doctorate from Nanyang Technological University (NTU).
Monday session 3
Phase separation and mobile noncoding RNA regulate leaf senescence.
Nam-Hai Chua
Temasek Life Sciences Laboratory, National University of Singapore
Nitrogen is an essential macronutrient that is absorbed by roots and stored in leaves, mainly as ribulose-1,5-bisphosphate carboxylase/oxygenase. To adapt to nitrogen deficiency (-N), leaf senescence facilitates nitrogen redistribution. As the key transcription factor of Arabidopsis thaliana senescence, ORESARA1 (ORE1) is required for nitrogen deficiency (-N) induced senescence. Here, two essential observations were made. First, we found that Arabidopsis MED19a associates with ORE1 to activate -N senescence-responsive genes. Disordered MED19a forms inducible nuclear condensates under -N that is regulated by decreasing MED19a lysine acetylation. MED19a carboxyl terminus (cMED19a) harbors a mixed-charged intrinsically disordered region (MC-IDR) required for ORE1 interaction and liquid-liquid phase separation (LLPS). Second, -N signals, which are initially perceived by roots, are subsequently propagated to shoots to trigger senescence; however, the mechanism of -N signal propagation remains underexplored. We found that ELF18-INDUCED LONG NONCODING RNA 1 (ELENA1) is -N inducible and attenuates -N induced senescence in Arabidopsis. Analysis of plants expressing ELENA1 promoter β-glucuronidase fusion gene showed that ELENA1 is transcribed specifically in roots under -N. Reciprocal grafting of WT and elena1 demonstrated that ELENA1 functions systemically. ELENA1 dissociates the MEDIATOR SUBUNIT 19a-ORESARA1 transcriptional complex thereby calibrating senescence progression. Our observations establish the systemic regulation of leaf senescence by a root-derived long noncoding RNA under -N in Arabidopsis.