New mechanism of dynamic regulation of growth and immunity in rape

On November 30, the Journal of molecular plant published on-line a Brassica miRNA regulations plant growth and immunity through distinct modes of action by Guo Huishan, research group of Institute of Microbiology, Chinese Academy of Sciences, and Duan Chengguo, research group of excellence and innovation center of molecular plant science, Chinese Academy of Sciences / Institute of plant physiology and ecology, Shanghai plant adversity center A 22 NT miRNA found in Brassica napus was reported to dynamically regulate the resistance and development of Brassica napus through different mechanisms In the face of adversity stress such as plant diseases and insect pests, plants often consume more metabolic resources to activate defense system to resist pathogen infection at the cost of inhibiting normal growth This phenomenon is called "tradeoff between growth and defense" Therefore, in crop breeding, how to coordinate the balance between growth and stress resistance has become a major challenge In the plant immune mechanism, immune receptor R protein recognizes the immune response induced by pathogenic effector protein and RNA silencing mediated by small RNA (including anti-virus RNA silencing and cross-border RNAi mediated anti fungal mechanism) are two important defense pathways If there is no pathogen infection, the high expression of R protein will induce the occurrence of auto immunity and lead to the serious inhibition of plant development Therefore, there is a reverse regulatory mechanism controlling the expression of R gene in plants Among them, miRNA mediated RNA silencing can control the expression level of R gene at the post transcriptional level and play an important role in plant autoimmune regulation MiRNA plays an important role in plant growth and development So, are there miRNAs in plants that regulate growth and development as well as immune resistance? If it can also respond to pathogen infection, the study of its molecular mechanism will have a very important guiding significance and application value for the "balance between growth and defense" of crop breeding Brassica napus belongs to Brassica of Cruciferae, which was called "Brassica" in ancient China It is a kind of oil-bearing crop with strong adaptability, wide use, high economic value and long cultivation history Its output ranks second only to soybean in the world oil-bearing crop production Rape is also an important oil crop and economic crop in China In agricultural production, virus is an important pathogen that seriously harms rape production, such as turnip mosaic virus (TuMV) It was found that mirna-mir1885, a 22 NT specific miRNA of Brassica napus, could target the R gene bratnl1 of TIR-NBS-LRR type, improve the expression level of bratnl1 and enhance the resistance of Brassica napus to TuMV The results suggest that mir1885 mediates the cleavage of bratnl1 to maintain the background level of immune activity In addition, mir1885 targets a bratir1 gene with only a TIR domain Mir1885 mediates the cleavage of bratir1 and produces tandem secondary siRNAs (phasirnas) One of the phasirnas, phasir130-4, can target bracp24, a gene related to flowering and photosynthesis This indicates that bratir1 is a TAS (trans acting Silencing) gene is involved in the regulation of flowering in Brassica napus, i.e down regulating bracp24 to promote the transformation of flowering stage Interestingly, the researchers found that the accumulation of mir1885 changed dynamically with different development stages It was maintained at a low level at seedling stage, reached a peak at flowering stage, and rapidly decreased to a very low level after flowering, which reflected the plant's immune activity at the background level through mir1885 / bratnl1 module at Seedling stage without infection, and maintained through mir1885 / bratir1 (phasir130-4) / bracp24 module at the same time Inhibit the early flowering of plants and promote the growth of nutrition The researchers also found that TuMV infection induced mir1885, through phasir130-4 mediated degradation of bracp24 to promote flowering; subtly, rape responded to TuMV infection by increasing the expression of bratnl1 to compensate for mir1885 mediated silencing inhibition, so that the plant was in an active epidemic free state In accordance with this, overexpression of mir1885 resulted in earlier flowering and smaller pods, while downregulation of mir1885 showed late flowering and larger pods This study revealed for the first time that plant miRNAs target immune receptor R genes and development related genes simultaneously through different mechanisms, dynamically regulate plant immunity and development, and respond to pathogen infection It reflects a kind of integrated response strategy adopted by plants in the face of interaction among normal growth, immune mechanism and pathogen infection.