A ubiquitin‐specific protease functions in regulating cell death and immune responses in rice

Abstract

Ubiquitin-specific proteases (UBPs) process deubiquitination in eukaryotic organisms and are widely involved in plant development and responses to environmental stress. However, their role in cell death and plant immunity remains largely unknown. Here, we identified a rice lesion mimic mutant (LMM) and cloned its causative gene, LMM22. Both dysfunction and overexpression of LMM22 gave rise to the hypersensitive response-like cell death, reactive oxygen species bursts, and activated defence responses. LMM22 encodes an active UBP that is localised to the endoplasmic reticulum (ER) and displays a constitutive expression pattern in rice.LMM22 interacts with SPOTTED LEAF 35 (SPL35), a coupling of ubiquitin conjugation to ER degradation domain-containing protein that is known to participate in ubiquitination and the regulation of cell death and disease response in rice. Additional analyses suggest that LMM22 can positively regulate and stabilise the abundance of SPL35 protein likely through its deubiquitination activity. These data therefore improve our understanding of the function of UBP in rice innate immune responses by demonstrating that LMM22 functions as a critical regulator of SPL35 in cell death and disease resistance.

Prospects for rice in 2050

“…Vo et al (2022) summarized recent advances in the understanding and engineering of ETI in rice, particularly on rice nucleotide‐binding and leucine‐rich repeat (NLR or NB‐LRR) family R proteins and effectors, and proposed promising strategies including using NLRome and Effectome studies to overcome challenges and improve rice immunity via engineering ETI (Vo et al, 2022). Zou et al (2023) characterized functions of an endoplasmic reticulum (ER)‐localized ubiquitin‐specific protease (UBP), LMM2, in rice cell death and innate immunity. The find that LMM2 can directly interact with SPL35, a coupling of ubiquitin conjugation to ER degradation domain‐containing protein that interacts with ubiquitin molecules, and maintain its stability (Zou et al, 2023).…”

“…Zou et al (2023) characterized functions of an endoplasmic reticulum (ER)‐localized ubiquitin‐specific protease (UBP), LMM2, in rice cell death and innate immunity. The find that LMM2 can directly interact with SPL35, a coupling of ubiquitin conjugation to ER degradation domain‐containing protein that interacts with ubiquitin molecules, and maintain its stability (Zou et al, 2023). Although how SPL35 is ubiquitinated and if ubiquitinated SPL35 is direct de‐ubiquitinated by LMM22 is not known, this study provided novel views on rice immunity.…”

The Hypersensitive Response to Plant Viruses

“…UPS is also involved in the degradation of stress proteins including NLRs, EDS1, and WRKY TFs in SA-induced NPR1 condensates (SINCs), promoting cell survival during HR [ 194 ]. Finally, deubiquitinases have been shown to play a critical role in limiting HR and cell death [ 195 , 196 ].…”

SPL50 negatively regulates cell death and disease resistance in rice

“…To date, an array of LMM genes has been elucidated, encoding proteins that span a diverse range of functions. These include the MEDIATOR SUBUNIT 16 (Zhang et al, 2023), the deubiquitinase OsLMP1 (Zou et al, 2023;Sun et al, 2022), receptor-like protein kinase SPL36 (Rao et al, 2021), translation factor OsWRKY19 (Du et al, 2021), ATP-citrate lyase SPL30 (Ruan et al, 2019), eukaryotic translation elongation factor 1 alpha (eEF1A)-like protein SPL33 (Wang et al, 2017), splicing factor 3b subunit SPL5 (Chen et al, 2012), and heat shock transcription factor SPL7 (Yamanouchi et al, 2003). Each of these genes plays a distinct and pivotal role in the intricate biological phenomena observed in plants, especially in underlining the mechanisms of disease resistance and PCD in rice.…”