The plant immune system is fundamental to plant survival in natural ecosystems and productivity in crop fields. Substantial evidence supports the prevailing notion that plants possess a two-tiered innate immune system, called pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). PTI is triggered by microbial patterns via cell surface-localized pattern-recognition receptors (PRRs), whereas ETI is activated by pathogen effector proteins via mostly intracellularly-localized receptors called nucleotide-binding, leucine-rich repeat proteins . CC-BY-NC-ND 4.

23The plant immune system is fundamental to plant survival in natural ecosystems and productivity 24 in crop fields. Substantial evidence supports the prevailing notion that plants possess a two-tiered 25 innate immune system, called pattern-triggered immunity (PTI) and effector-triggered immunity 26 (ETI). PTI is triggered by microbial patterns via cell surface-localized pattern-recognition 27 receptors (PRRs), whereas ETI is activated by pathogen effector proteins via mostly 28 intracellularly-localized receptors called nucleotide-binding, leucine-rich repeat proteins 29 50 from both pathogenic and nonpathogenic microbes. NLRs, on the other hand, are intracellular 51 proteins that sense pathogen-derived effector proteins inside the plant cell and can be further 52 classified into the coiled coil (CC)-type, Toll/interleukin-1 receptor (TIR)-type, or RPW8 (CCR)-53 type, depending on their N-terminal domain 7 . However, PRR-and NLR-mediated signaling 54 pathways result in many similar downstream immune outputs, including defense gene 55 expression, production of ROS and callose deposition at the plant cell wall 8,9 . The underlying 56 reason is not clear and mechanistic relationship between the two immune pathways remains 57 largely enigmatic. Notably, while many PRR signaling components have been identified and 58 anti-pathogen mechanisms described, the downstream signaling events in ETI and how ETI halts 59 pathogen growth still remain poorly understood, despite recent breakthroughs in the 60 understanding of NLR protein structures and activities 10-13 . 61 62 Requirement of PRR/co-receptors for ETI 63 Using Arabidopsis thaliana-Pseudomonas syringae pathosystem, we accidentally discovered a 64 striking and unexpected role of PRR/co-receptors in ETI. Specifically, an "avirulent", ETI-65 eliciting bacterial strain, P. syringae pv. tomato (Pst) DC3000(avrRpt2), which activates RPS2 66 (Resistance to P. syringae 2)-dependent ETI in wild-type Col-0 plants 14,15 , failed to elicit 67 effective ETI in two separate PRR/co-receptor Arabidopsis mutants, fls2/efr/cerk1 (fec) and 68 bak1/bkk1/cerk1 (bbc) mutants, which are mutated in major PRR/co-receptors recognizing 69 bacteria-associated molecular patterns 16 . As shown in Fig. 1a, the fec and bbc mutants did not 70 mount an effective ETI against Pst DC3000(avrRpt2). To determine whether a requirement of 71 PRR/co-receptors for ETI is specific to Pst DC3000(avrRpt2) or is a more general phenomenon, 72 we tested two other ETI-triggering "avirulent" effectors, AvrPphB and AvrRps4, which are 73 recognized by RPS5 17 and RPS4 18 , respectively, in Arabidopsis Col-0 accession. We found that 74 the compromised ETI phenotype in fec and bbc mutants held true for both AvrPphB and 75 AvrRps4 (Extended Data Fig. 1), suggesting a potentially broad role of PRR/co-receptors in ETI 76 pathways. We subsequently focused on AvrRpt2-triggered ETI for in-depth characterization. 77 Hypersensitive response (HR), manifested by fast cell death under high bacterial inoculum, is a...

Doublesex is highly conserved and sex-specifically spliced in insect sex-determination pathways, and its alternative splicing (AS) is regulated by Transformer, an exonic splicing activator, in the model system of Drosophila melanogaster. However, due to the lack of a transformer gene, AS regulation of doublesex remains unclear in Lepidoptera, which contain the economically important silkworm Bombyx mori and thousands of agricultural pests. Here, we use yeast three-hybrid system to screen for RNA-binding proteins that recognize sex-specific exons 3 and 4 of silkworm doublesex (Bm-dsx); this approach identified BxRBP1/Lark binding to the exon 3, and BxRBP2/TBPH and BxRBP3/Aret binding to the exon 4. Investigation of tissues shows that BxRBP1 and BxRBP2 have no sex specificity, but BxRBP3 hasthree of its four isoforms are expressed with a sex-bias. Using novel sex-specific silkworm cell lines, we find that BxRBP1 and BxRBP3 directly interact with each other, and cooperatively function as splicing repressors. Over-expression of BxRBP1 and BxRBP3 isoforms efficiently inhibits splicing of the exons 3 and 4 in the female-specific cells and generates the male-specific isoform of Bm-dsx. We also demonstrate that the sex-determination upstream gene Masc regulates alternatively transcribed BxRBP3 isoforms. Thus, we identify a new regulatory mechanism of doublesex AS in the silkworm, revealing an evolutionary divergence in insect sex-determination.

The occurrence of plant disease is determined by interactions among host, pathogen and climate conditions. Air humidity has long been recognized to profoundly influence diseases in the phyllosphere, and high air humidity (e.g., after rain falls) is known as a prerequisite for numerous disease outbreaks in the field. However, the molecular basis of how high humidity interferes with plant resistance mechanisms to favor disease remained elusive. Here we show that high humidity is associated with an immune-compromised status of plants, revealed by lower expression of defense genes during bacterial infection of Arabidopsis plants. Examination of humidity is effect on individual immune pathways showed that the accumulation and signaling of salicylic acid (SA), an essential hormone conferring plant resistance against infectious microbes, are significantly inhibited under high humidity. Surprisingly, NPR1 protein, an SA receptor and central transcriptional co-activator of SA-responsive genes, accumulated to a significantly higher level in the nucleus under high humidity. Further investigation indicated a decreased binding affinity of NPR1 protein to the target gene promoter, suggestive of an inactive nature of NPR1, under high humidity and an impaired ubiquitination and degradation of NPR1 protein, likely due to down-regulation of Cullin 3-mediated cellular ubiquitination pathway and 26S proteasome pathway under high humidity. Our study uncovers disruption of NPR1 protein turnover as a major mechanism, by which high humidity dampens plant immune strength against pathogens, and provides new insights into the long-observed air humidity influence on diseases in nature.