Molecular Pathogens 2024, Vol.15, No.5, 237-245 http://microbescipublisher.com/index.php/mp 240 Figure 1 Map-based cloning of Xa7(Adopted from Chen et al., 2021) Image caption: (A) Physical map of Xa7 on rice chromosome 6 based on the reference genome of Nipponbare (Nip); n refers to the total number of BB-susceptible F2 plants used for fine mapping; the number under each marker represents the number of recombinants detected by the corresponding marker. (B–D) Physical maps of Xa7 based on the rice varieties (B) IR24, (C) IRBB7, and (D) Zhen-hui 084 (ZH084). Maps were built using contigs of clones isolated from the genomic libraries of the corresponding varieties. (E) The 28 kb overlapping region between the 116-kb Xa7 mapping region and the 107 kb deletion in a BB-susceptible mutant, zsm-2, mutagenized from ZH084. (F) Predicted genes (G1 to G7) in the 28-kb overlapping region and relative positions and sizes of the four fragments (C1 to C4) used for complementation transformation in Zhonghua 11 (ZH11). (G) Contigs and sizes of subclones (C2S1, C1S1 to C1S7) used for the transgenic complementation test in ZH11. Numbers under the line represent positions relative to the start codon (atg) of the Xa7 gene. Negative numbers refer to positions before atg, and positive numbers refer to positions starting at atg. taa refers to the stop codon of Xa7, and the sequence from atg to taa is 342 bp in length. (H) Leaves inoculated with Xoo strain PXO86. Photographs were taken 2 weeks after inoculation. Nip, IR24, and ZH11 are BB-susceptible rice varieties. IRBB7 and ZH084 are Xa7-containing rice varieties. zsm-2 refers to a BB-susceptible mutant mutagenized from ZH084. C1 to C4, C1S1 to C1S7, and C2S1 are the transgenic complementation lines of ZH11. Bar, 2 cm (Adopted from Chen et al., 2021) 5 Challenges and Countermeasures for Disease Resistance Persistence 5.1 Research on the durability of disease resistance genes The durability of disease resistance genes is a critical factor in the long-term management of bacterial blight in rice. Research has shown that resistance genes can lose their effectiveness due to the emergence of new virulent strains of the pathogen. For instance, the Xa10 gene, which confers resistance to Xanthomonas oryzae pv. oryzae, Xoo (Xoo), was modified to create Xa10 (E5) to provide broad-spectrum and durable resistance. This modification involved the addition of multiple effector binding elements (EBEs) to the promoter region, allowing the gene to respond to various TAL effectors from different Xoo strains (Zeng et al., 2015). However, the continuous
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