Plants need to strictly control the expression of immune genes in the process of growth and development, so as to maintain the balance between plant growth and resistance. Uncontrolled expression will directly damage the growth and development of plants, which we call autoimmunity, and this phenomenon also exists widely in humans. Recent studies have shown that transcriptional regulation is necessary, but not always effective, for the regulation of immune genes. In this case, adding a translation regulatory element uORF can further control the translation of immune genes. When plants encounter pathogen invasion, multiple molecular levels in plant cells are reprogrammed and adjusted to cope with pathogen invasion. Cells are faced with a large number of immune transcriptomes rapidly flowing into the translation pool, and an effective immune response requires cells to regulate the translation efficiency of immune genes at a global level. Finding and identifying global translational reprogramming factors in the process of plant immunity will clarify the physiological significance of translational regulation in immune response.
On February 16, 2023, Guoyong Xu's team from Wuhan University published a research paper entitled "Plant HEM1 specifies a condensation domain to control immune gene translation" online in Nature Plants, revealing a new mechanism for the regulation of plant immune translation.
Through forward genetic screening, this study identified HEM1 (or NAP1), a key member that regulates Actin polymerization, as a key factor in translation regulation. The over-translation of HEM1-restricted immune genes was further confirmed by the improved ribosome footprinting technique. This function is independent of the conventional understanding that HEM1 regulates the Actin pathway through the WAVE complex, suggesting that HEM1 regulates translation through other pathways. Further studies found that HEM1 interacts with a large number of translation factors to form condensate, and depends on the plant-specific condensation domain LCD. In vivo and in vitro biochemical experiments demonstrated that HEM1 is a phase transition protein that responds to the stimulation of immune signals through plant-specific LCD. Through the developed CRISPR-walking technology, the C-terminal sequence of the HEM1 gene was knocked out, and it was found that only the mutant that precisely knocked out the LCD did not affect the plant Actin-related developmental phenotype, but showed similar translational regulation and immune response phenotypes to the complete deletion mutant hem1.
In summary, in plant effector-triggered immunity (ETI), HEM1 interacts with a large number of translation factors through the plant-specific LCD domain to form condensate, and this condensate -forming mechanism plays an important role in plant immunity. The formation of HEM1 condensate effectively inhibits the over-translation of immune genes, thereby balancing tissue health and resistance to prevent tissue damage caused by excessive activation of plant immunity.
Reference:
Zhou, Y., Niu, R., Tang, Z. et al. Plant HEM1 specifies a condensation domain to control immune gene translation. Nat. Plants 9, 289–301 (2023). https://doi.org/10.1038/s41477-023-01355-7
