The unconventional resistance protein PTR recognizes the Magnaporthe oryzae effector AVR-Pita in an allele-specific manner.

Blast disease caused by the fungus Magnaporthe oryzae is one of the most devastating rice diseases. Disease resistance genes such as Pi-ta or Pi-ta2 are critical in protecting rice production from blast. Published work reports that Pi-ta codes for a nucleotide-binding and leucine-rich repeat domain protein (NLR) that recognizes the fungal protease-like effector AVR-Pita by direct binding. However, this model was challenged by the recent discovery that Pi-ta2 resistance, which also relies on AVR-Pita detection, is conferred by the unconventional resistance gene Ptr, which codes for a membrane protein with a cytoplasmic armadillo repeat domain. Here, using NLR Pi-ta and Ptr RNAi knockdown and CRISPR/Cas9 knockout mutant rice lines, we found that AVR-Pita recognition relies solely on Ptr and that the NLR Pi-ta has no role in it, indicating that it is not the Pi-ta resistance gene. Different alleles of Ptr confer different recognition specificities. The A allele of Ptr (PtrA) detects all natural sequence variants of the effector and confers Pi-ta2 resistance, while the B allele of Ptr (PtrB) recognizes a restricted set of AVR-Pita alleles and, thereby, confers Pi-ta resistance. Analysis of the natural diversity in AVR-Pita and of mutant and transgenic strains identified one specific polymorphism in the effector sequence that controls escape from PtrB-mediated resistance. Taken together, our work establishes that the M. oryzae effector AVR-Pita is detected in an allele-specific manner by the unconventional rice resistance protein Ptr and that the NLR Pi-ta has no function in Pi-ta resistance and the recognition of AVR-Pita.

The RLCK subfamily VII-4 controls pattern-triggered immunity and basal resistance to bacterial and fungal pathogens in rice.

Receptor-like cytoplasmic kinases (RLCKs) mediate the intracellular signaling downstream of pattern-recognition receptors (PRRs). Several RLCKs from subfamily VII of rice (Oryza sativa) have important roles in plant immunity, but the role of RLCK VII-4 in pattern-triggered immune (PTI) signaling and resistance to pathogens has not yet been investigated. Here, we generated by multiplex clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9-mediated genome editing rice sextuple mutant lines where the entire RLCK VII-4 subfamily is inactivated and then analyzed the resulting lines for their response to chitin and flg22 and for their immunity to Xanthomonas oryzae pv. oryzae (Xoo) and Magnaporthe oryzae. Analysis of the rlckvii-4 mutants revealed that they have an impaired reactive oxygen system burst and reduced defense gene expression in response to flg22 and chitin. This indicates that members of the rice RLCK VII-4 subfamily are required for immune signaling downstream of multiple PRRs. Furthermore, we found that the rice RLCK VII-4 subfamily is important for chitin-induced callose deposition and mitogen-activated protein kinase activation and that it is crucial for basal resistance against Xoo and M. oryzae pathogens. This establishes that the RLCK VII-4 subfamily has critical functions in the regulation of multiple PTI pathways in rice and opens the way for deciphering the precise role of its members in the control of rice PTI.

Genome-wide analysis of annexin gene family in Schrenkiella parvula and Eutrema salsugineum suggests their roles in salt stress response.

Annexins (Anns) play an important role in plant development, growth and responses to various stresses. Although Ann genes have been characterized in some plants, their role in adaptation mechanisms and tolerance to environmental stresses have not been studied in extremophile plants. In this study, Ann genes in Schrenkiella parvula and Eutrema salsugineum were identified using a genome-wide method and phylogenetic relationships, subcellular distribution, gene structures, conserved residues and motifs and also promoter prediction have been studied through bioinformatics analysis. We identified ten and eight encoding putative Ann genes in S. parvula and E. salsugineum genome respectively, which were divided into six subfamilies according to phylogenetic relationships. By observing conservation in gene structures and protein motifs we found that the majority of Ann members in two extremophile plants are similar. Furthermore, promoter analysis revealed a greater number of GATA, Dof, bHLH and NAC transcription factor binding sites, as well as ABRE, ABRE3a, ABRE4, MYB and Myc cis-acting elements in compare to Arabidopsis thaliana. To gain additional insight into the putative roles of candidate Ann genes, the expression of SpAnn1, SpAnn2 and SpAnn6 in S. parvula was studied in response to salt stress, which indicated that their expression level in shoot increased. Similarly, salt stress induced expression of EsAnn1, 5 and 7, in roots and EsAnn1, 2 and 5 in leaves of E. salsugineum. Our comparative analysis implies that both halophytes have different regulatory mechanisms compared to A. thaliana and suggest SpAnn2 gene play important roles in mediating salt stress.