Based on the high sequence similarity between the SlSERK3A and SlSERK3B catalytic domains, and their redundant role in BR signaling, we hypothesis that SlSERK3A can also trans-phosphorylate SlBRI. Since SlSERK3 is required for signaling and immunity mediated by the tomato RLP LeEix2 and Ve1, respectively, it is likely that SlSERK3A or SlSERK3B individually or together are capable of trans-phosphorylating multiple receptors in a manner similar to BAK1. Both SlSERK3A and SlSERK3B formed flg22-dependent complex with SlFLS2. Several AtSERK members are able to heterodimerize with FLS2, albeit at variable levels of association, in ligand dependent manner. Further Tubeimoside-I investigations should reveal whether SlSERK3A and SlSERK3B form a heterodimer in this interaction and whether SlFLS2 is also able to heterodimerize with SlSERK1. The ability of SlSERK3A and SlSERK3B to form a ligand induced complex with SlFLS2 suggested a role for these two SERK paralogs in FLS2-dependent signaling. Indeed, both SlSERK3A and SlSERK3B have non-redundant functions in flg22-induced ROS production and activation of defense related genes. Among Arabidopsis SERK members, a similar function is only demonstrated for BAK1. Only bak1 single mutants are compromised in flg22-induced ROS and none of the remaining individual serk null mutants are impaired in ligand induced ROS production. A minor role in flg22-induced ROS production was uncovered for bkk1 in the bak1-5 bkk1 double mutant. Taken together, this information indicates that SlSERK3A and SlSERK3B have BAK1related functions and seem to be true orthologs of this Arabidopsis gene. Indeed, in complementation experiments either SlSERK3A or SlSERK3B partially rescued the bak1 mutant 4-(Benzyloxy)phenol phenotype. The lack of full bak1 complementation is likely due to sequence divergence between these Arabidopsis and tomato orthologs. Similar to Arabidopsis, the expression of SlCPD in tomato is down-regulated by exogenous application of BR via a presumed negative feedback mechanism. The attenuation of SlCPD responsiveness to exogenous BR application in the SlSERK3A and SlSERK3B co-silenced plants, and not in the individual SlSERK3A or SlSERK3B silenced plants, indicates that SlSERK3A and SlSERK3B have redundant function in BR signaling. Since the SlSERK3A and SlSERK3B co-silenced plants had residual BR signaling competence, it suggests that the only other family member SlSERK1 also contributes to BR response. Based on CPD expression analysis in Arabidopsis, it is not clear the contribution of BKK1/SERK4 to BR signaling as BR effect on CPD expression have been analyzed in the double mutant bak1 serk1 or the triple mutant bak1 bkk1 serk1 and not in the double mutant bak1 bkk1. Nonetheless, our results show that SlSERK3A and SlSERK3B contribute to most of the BR effect on CPD expression in tomato. In summary, our work provides functional characterization of SlSERK3A and SlSERK3B in an important crop and demonstrates differences and similarities in the role of BAK1 and SlSERK3A and SlSERK3B paralogs in immunity and BR signaling. This work also provides a foundation for future characterization of PTI against RKN in roots. Melatonin is a versatile molecule that, since its 1958 discovery in bovine pineal glands, has been found across kingdom lines including 
bacteria, fungi, and plants. Its numerous and diverse functions include regulating circadian rhythms and seasonal reproduction cycles, promoting sleep, preventing diabetes, attenuating cancer cell proliferation, and enhancing immunity.