Phytophthora infestans (P. infestans) recently caused epidemics of tomato late blight. Our study aimed to identify the function of the SlMYBS2 gene in response to tomato late blight. To further investigate the function of SlMYBS2 in tomato resistance to P. infestans, we studied the effects of SlMYBS2 gene knock out. The SlMYBS2 gene was knocked out by CRISPR-Cas9, and the resulting plants (SlMYBS2 gene knockout, slmybs2-c) showed reduced resistance to P. infestans, accompanied by increases in the number of necrotic cells, lesion sizes, and disease index. Furthermore, after P. infestans infection, the expression levels of pathogenesis-related (PR) genes in slmybs2-c plants were significantly lower than those in wild-type (AC) plants, while the number of necrotic cells and the accumulation of reactive oxygen species (ROS) were higher than those in wild-type plants. Taken together, these results indicate that SlMYBS2 acts as a positive regulator of tomato resistance to P. infestans infection by regulating the ROS level and the expression level of PR genes.

Leaves, which are the most important organs of plants, can not only fix carbon sources through photosynthesis, but also absorb nutrients through transpiration. Leaf development directly determines the growth, flowering and fruiting of plants. There are many factors that affect leaf development, such as the growth environment, gene expression, and hormone synthesis. In this study, tomatoes were used to study the role of the transcription factor Solanum lycopersicum salt-related MYB1-like (SlSRM1-like) in the development of tomato leaves. Loss-of-function of the SlSRM1-like gene mediated by clustered, regularly interspaced, short palindromic repeat (CRISPR)/CRISPR-associated 9 (Cas9) resulted in abnormal tomato leaf morphology, including thinner leaves, wrinkled edges, raised veins, disordered edge veins, and left and right asymmetry. An analysis of the transcription levels of genes related to leaf development revealed that the expression of these genes was significantly altered in the SlSRM1-like mutants (SlSRM1-like-Ms). Moreover, the SlSRM1-like gene was expressed at higher transcription levels in young tissues than in old tissues, and its expression was also induced in response to auxin. In addition, the transcription levels of genes related to the auxin pathway, which regulates tomato growth and development, were severely affected in the SlSRM1-like-Ms. Therefore, it is hypothesized that the SlSRM1-like gene functions in the regulation of tomato leaf development through the auxin-related pathway. In this study, we successfully knocked out the SlSRM1-like gene in the tomato variety Ailsa Craig using CRISPR technology and found that knockout of the SlSRM1-like gene resulted in abnormal development of tomato leaves. Further research indicated that SlSRM1-like regulated tomato leaf development through auxin-related pathways. The results provide an important reference for the functional study of other SRM1-like genes in plants and provide new insights into the regulation of leaf development in tomato and other plants.