The Two Tomato Ubiquitin E1 Enzymes Play Unequal Roles in Host Immunity

Area of Science:

• Plant molecular biology
• Ubiquitin-proteasome system
• Plant immunity

Background:

• Plants possess multiple ubiquitin-activating enzymes (E1s/UBAs) with unclear functional divergence.
• Understanding E1 enzyme roles is crucial for plant development and defense mechanisms.

Purpose of the Study:

• To investigate the distinct roles of two tomato E1 enzymes, SlUBA1 and SlUBA2, in plant development and immunity.
• To elucidate the molecular mechanisms underlying differential E1 enzyme function.

Main Methods:

• Gene silencing (knockdown) of SlUBA1 and SlUBA2 in tomato (Solanum lycopersicum).
• Assessing plant growth, development, and immunity against Pseudomonas syringae pv. tomato (Pst).
• Analyzing E1-E2 enzyme charging efficiencies and domain swapping experiments.

Main Results:

• SlUBA1 and SlUBA2 exhibit distinct roles in tomato development; simultaneous silencing leads to plant death.
• SlUBA2, but not SlUBA1, is essential for immunity against Pst.
• Differential E2-charging efficiencies between SlUBA1 and SlUBA2 were linked to their C-terminal ubiquitin-folding domains (UFDs).

Conclusions:

• Tomato utilizes dual ubiquitin-activating systems (DUAS) with specialized functions.
• The SlUBA2-group IV E2 module is critical for plant defense against bacterial pathogens.
• Differential E1 enzyme function is conserved in plants, as suggested by Arabidopsis homologues.