Jihong Xing

The Kynurenine 3-Monooxygenase Encoding Gene, BcKMO, Is Involved in the Growth, Development, and Pathogenicity of Botrytis cinerea

A pathogenic mutant, BCG183, was obtained by screening the T-DNA insertion library of Botrytis cinerea. A novel pathogenicity-related gene BcKMO, which encodes kynurenine 3-monooxygenase (KMO), was isolated and identified via thermal asymmetric interlaced PCR, bioinformatics analyses, and KMO activity measurement. The mutant BCG183 grew slowly, did not produce conidia and sclerotia, had slender hyphae, and presented enhanced pathogenicity. The phenotype and pathogenicity of the BcKMO-complementing mutant (BCG183/BcKMO) were similar to those of the wild-type (WT) strain. The activities of polymethylgalacturonase, polygalacturonase, and toxins were significantly higher, whereas acid production was significantly decreased in the mutant BCG183, when compared with those in the WT and BCG183/BcKMO. Moreover, the sensitivity of mutant BCG183 to NaCl and KCl was remarkably increased, whereas that to fluconazole, Congo Red, menadione, H2O2, and SQ22536 and U0126 [cAMP-dependent protein kinase (cAMP) and mitogen-activated protein kinase (MAPK) signaling pathways inhibitors, respectively] were significantly decreased compared with the other strains. Furthermore, the key genes involved in the cAMP and MAPK signaling pathways, Pka1, Pka2, PkaR, Bcg2, Bcg3, bmp1, and bmp3, were significantly upregulated or downregulated in the mutant BCG183. BcKMO expression levels were also upregulated or downregulated in the RNAi mutants of the key genes involved in the cAMP and MAPK signaling pathways. These findings indicated that BcKMO positively regulates growth and development, but negatively regulates pathogenicity of B. cinerea. Furthermore, BcKMO was found to be involved in controlling cell wall degrading enzymes activity, toxins activity, acid production, and cell wall integrity, and participate in cAMP and MAPK signaling pathways of B. cinerea.

T1N6_22 positively regulates Botrytis cinerea resistance but negatively regulates Pseudomonas syringae pv. tomato DC3000 resistance in Arabidopsis thaliana

ABSTRACT T1N6_22, a short-chain dehydrogenase/reductase family protein, was identified as a positive regulator in Arabidopsis thaliana resistance against Botrytis cinerea and Alternaria brassicae in our preliminary study. In this study, we found that the expression levels of the T1N6_22 gene were induced and up-regulated in A. thaliana ecotype Columbia (Col-0) after B. cinerea and Pseudomonas syringae pv. tomato DC3000 inoculation. Compared with the Col-0 and t1n6_22/T1N6_22 plants, the expression of PAL, PR4, PPO, SOD and CAT genes were down-regulated in the t1n6_22 plants. In Col-0 plants treated with salicylic acid (SA) and the SA analogue benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), the expression levels of T1N6_22 were significantly enhanced, whereas the expression levels of T1N6_22 were reduced by jasmonic acid treatment. Meanwhile, the t1n6_22 mutant exhibited enhanced resistance, whereas the wild-type Col-0 and complemented plants (t1n6_22/T1N6_22) showed susceptibility to Pst DC3000. After inoculation with B. cinerea and Pst DC3000, the expression levels of defence-related genes PR1, PR3, PR5, NPR1 and PDF1.2 in t1n6_22 were significantly different from those in Col-0 and t1n6_22/T1N6_22 plants. Taken together, the T1N6_22 gene played a negative role in Arabidopsis resistance to Pst DC3000. The T1N6_22 gene may be involved in the regulation of salicylic acid and jasmonic-acid–signalling pathways to affect the resistance of Arabidopsis to B. cinerea and Pst DC3000.

Functional analysis of BT4 of Arabidopsis thaliana in resistance against Botrytis cinerea

Botrytis cinerea is a fungus with a necrotrophic lifestyle attacking over 200 crop hosts worldwide, resulting in significant economic losses. At present, the molecular and cellular mechanisms involved in plant resistance to B. cinerea and their genetic control are poorly understood. The Arabidopsis BT4 gene was previously isolated by DDRT-PCR under B. cinerea infection. However a role for BT4 in defense signaling has not been described to date. Compared with wild-type (wt) Col-0, the loss-of-function mutant of BT4 showed increased susceptibility to B. cinerea and enhanced expression of some defense-related genes such as PR1, SOD1, PPO, PAL, POD and CAT. However, expression of other defense-related genes such as NPR1, PR4 and PDF1.2 were repressed in the mutant compared with wt plants. In addition, transgenic lines overexpressing BT4 restored resistance to B. cinerea. Taken together, our results indicate that BT4 play an important role in Arabidopsis in resistance to B. cinerea perhaps by regulating the expression of defense-related genes in response to SA and JA signaling pathways.