Expression of the Arabidopsis Mg-chelatase H subunit alleviates iron deficiency-induced stress in transgenic rice

Abstract

The most common symptom of iron (Fe) deficiency in plants is leaf chlorosis caused by impairment of chlorophyll biosynthesis. Magnesium (Mg)-chelatase H subunit (CHLH) is a key component in both chlorophyll biosynthesis and plastid signaling, but its role in Fe deficiency is poorly understood. Heterologous expression of the Arabidopsis thaliana Mg-chelatase H subunit gene (AtCHLH) increased Mg-chelatase activity by up to 6-fold and abundance of its product, Mg-protoporphyrin IX (Mg-Proto IX), by 60–75% in transgenic rice (Oryza sativa) seedlings compared to wild-type (WT) controls. Noticeably, the transgenic seedlings showed alleviation of Fe deficiency symptoms, as evidenced by their less pronounced leaf chlorosis and lower declines in shoot growth, chlorophyll contents, and photosynthetic efficiency, as indicated by Fv/Fm and electron transport rate, compared to those in WT seedlings under Fe deficiency. Porphyrin metabolism was differentially regulated by Fe deficiency between WT and transgenic seedlings, particularly with a higher level of Mg-Proto IX in transgenic lines, showing that overexpression of AtCHLH reprograms porphyrin metabolism in transgenic rice. Leaves of Fe-deficient transgenic seedlings exhibited greater upregulation of deoxymugineic acid biosynthesis-related genes (i.e., NAS, NAS2, and NAAT1), YSL2 transporter gene, and Fe-related transcription factor genes IRO2 and IDEF2 than those of WT, which may also partly contribute to alleviating Fe deficiency. Although AtCHLH was postulated to act as a receptor for abscisic acid (ABA), exogenous ABA did not alter the phenotypes of Fe-deficient WT or transgenic seedlings. Our study demonstrates that modulation of porphyrin biosynthesis through expression of AtCHLH in transgenic rice alleviates Fe deficiency-induced stress, suggesting a possible role for CHLH in Fe deficiency responses.

Effects of nano urea on growth and gene expression ofArabidopsis thalianain hydroponics

“…CHLI1 is a subunit of the heterotrimeric Mg-chelatase, a key regulatory enzyme in the chlorophyll biosynthesis pathway that catalyzes the conversion of protoporphyrin IX to magnesium protoporphyrin IX in the presence of Mg 2+ and ATP. (Tran et al, 2023). ChlI stabilizes and activates the heterometric Mg-chelatase by folding and stabilizing the ChlD subunit (Walker and Willows, 1997; Gibson et al, 1999; Gräfe et al, 1999; Rissler et al, 2002).…”

Salt Stress-Induced Modulation of Porphyrin Biosynthesis, Photoprotection, and Antioxidant Properties in Rice Plants (Oryza sativa)

“…The observed changes in metabolic flux within the Mg branch under salt stress match the transcript levels of CHLD , CHLH , CHLI , and PORB ( Figure 5 B), indicating that the decrease in Mg-porphyrins results partially from the downregulation of these genes. Other abiotic stresses, including drought, chilling, and iron deficiency stress, also affect the chlorophyll biosynthetic pathway by reducing metabolite levels [ 12 , 13 , 14 ]. The scavenging of phototoxic chlorophyll precursors in NaCl-treated seedlings seems to be essential to cope with their excited-state dynamics, thereby mitigating salt-stress-induced oxidative damage.…”

“…In plants, porphyrins are essential in various processes, including light harvesting, energy transfer, detoxification, and signal transduction [ 9 , 10 ]. The regulation of porphyrin biosynthesis under various abiotic stresses, including iron deficiency, chilling, and drought, has been reported in previous studies [ 12 , 13 , 14 ]; however, its regulatory mechanism under salt stress has not yet been characterized.…”