AUTHOR=Shen Wangxin , Feng Zhiming , Hu Keming , Cao Wenlei , Li Mengchen , Ju Ran , Zhang Yafang , Chen Zongxiang , Zuo Shimin 

TITLE=Tryptamine 5-Hydroxylase Is Required for Suppression of Cell Death and Uncontrolled Defense Activation in Rice

JOURNAL=Frontiers in Sustainable Food Systems

VOLUME=6

YEAR=2022

URL=https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2022.857760

DOI=10.3389/fsufs.2022.857760

ISSN=2571-581X

ABSTRACT=<p>Lesion-mimic mutants are useful materials to dissect mechanisms controlling programmed cell death (PCD) and defense response in plants. Although dozens of lesion-mimic mutant genes have been identified in plants, the molecular mechanisms underlying PCD and defense response remain to be extensively elucidated. Here, we identified a rice lesion mimic mutant, named <italic>lesion mimic 42</italic> (<italic>lm42</italic>), from an ethylmethylsulfone (EMS)-induced mutant population. The <italic>lm42</italic> mutant displayed flame-red spots on the leaves and sheaths at the 3-leaf developmental stage and exhibited impaired photosynthetic capacity with decreased chlorophyll content and decomposed chloroplast thylakoids. The lesion development of <italic>lm42</italic> was light- and temperature-dependent. We identified a single base mutation (T38A), changing a Leu to Gln, in the first exon of <italic>LOC_Os12g16720</italic> (<italic>LM42</italic>), which encodes a tryptamine 5-hydroxylase, by map-based cloning. We carried out transgenic complementation to confirm that this mutation caused the <italic>lm42</italic> phenotype. We further knocked out the <italic>LM42</italic> gene by CRISPR/Cas9 to recreate the <italic>lm42</italic> phenotype. <italic>LM42</italic> is highly expressed in leaves, leaf sheaths and roots. Loss-of-function of <italic>LM42</italic> activated expression of ROS-generating genes and inhibited expression of ROS-scavenging genes, leading to ROS accumulation and eventually cell death. Furthermore, its disruption induced expression of defense-response genes and enhanced host resistance to both fungal pathogen <italic>Magnaporthe oryzae</italic> and bacterial pathogen <italic>Xanthomonas oryzae pv. oryzae</italic>. Our transcriptomic data suggested that the way <italic>lm42</italic> led to lesion-mimic was probably by affecting ribosome development. Overall, our results demonstrate that tryptamine 5-hydroxylase-coding gene <italic>LM42</italic> is required for suppression of cell death and uncontrolled activation of defense responses in rice.</p>