The Photorespiratory Arabidopsis shm1 Mutant Is Deficient in SHM1

Abstract

Mitochondrial serine hydroxymethyltransferase (SHMT), combined with glycine decarboxylase, catalyzes an essential sequence of the photorespiratory C 2 cycle, namely, the conversion of two molecules of glycine into one molecule each of CO 2 , NH 4 1 , and serine. The Arabidopsis (Arabidopsis thaliana) mutant shm (now designated shm1-1) is defective in mitochondrial SHMT activity and displays a lethal photorespiratory phenotype when grown at ambient CO 2 , but is virtually unaffected at elevated CO 2 . The Arabidopsis genome harbors seven putative SHM genes, two of which (SHM1 and SHM2) feature predicted mitochondrial targeting signals. We have mapped shm1-1 to the position of the SHM1 gene (At4g37930). The mutation is due to a G / A transition at the 5# splice site of intron 6 of SHM1, causing aberrant splicing and a premature termination of translation. A T-DNA insertion allele of SHM1, shm1-2, and the F 1 progeny of a genetic cross between shm1-1 and shm1-2 displayed the same conditional lethal phenotype as shm1-1. Expression of wild-type SHM1 under the control of either the cauliflower mosaic virus 35S or the SHM1 promoter in shm1-1 abrogated the photorespiratory phenotype of the shm mutant, whereas overexpression of SHM2 or expression of SHM1 under the control of the SHM2 promoter did not rescue the mutant phenotype. Promoter-b-glucuronidase analyses revealed that SHM1 is predominantly expressed in leaves, whereas SHM2 is mainly transcribed in the shoot apical meristem and roots. Our findings establish SHM1 as the defective gene in the Arabidopsis shm1-1 mutant.

Serine Acts as a Metabolic Signal for the Transcriptional Control of Photorespiration-Related Genes in Arabidopsis

“…Furthermore, these changes were not persistent over the whole analyzed period and appeared solely at one or two specific time points (Supplemental Table S2). Moreover, if compared with the strong alterations observed with other photorespiratory mutants Voll et al, 2006;Engel et al, 2007;Collakova et al, 2008;Timm et al, 2012b;Eisenhut et al, 2013), these metabolic changes are of a very moderate character, confirming the suitability of hpr1 as a model to study the direct feedback of a slightly and specifically reduced internal carbon flow on the regulation of photorespiration.…”

Mitochondrial and Nuclear Localization of a Novel Pea Thioredoxin: Identification of Its Mitochondrial Target Proteins

“…This enzyme involved in the photorespiratory pathway appears particularly susceptible to oxidative damage induced by drought and chilling (Taylor et al, 2002). Similarly, SHMT activity is a key enzyme in the photorespiratory event, and the shm1-1 mutant of Arabidopsis, defective in SHMT activity, has been shown to display a lethal photorespiratory phenotype when grown at ambient CO 2 (Voll et al, 2006). In this context, it would be very interesting to analyze the role of PsTrxo1 in the photorespiratory events in response to oxidative damage situations such as those induced by NaCl and water stress.…”

Systematic Mutagenesis of Serine Hydroxymethyltransferase Reveals an Essential Role in Nematode Resistance

“…The Arabidopsis mitochondrial SHMT is encoded by AtSHM1 and is required for the proper functioning of photorespiration (Somerville and Ogren, 1981;Voll et al, 2006). Its ortholog in rice (Oryza sativa) is OsSHM1 (Wang et al, 2015;Wu et al, 2015).…”