Abstract
BackgroundIron (Fe) is an essential micronutrient for plants. Utilization of Fe deficiency-tolerant rootstock is an effective strategy to prevent Fe deficiency problems in fruit trees production. Malus halliana is an apple rootstock that is resistant to Fe deficiency; however, few molecular studies have been conducted on M. halliana.ResultsTo evaluate short-term molecular response of M. halliana leaves under Fe deficiency condition, RNA sequencing (RNA-Seq) analyses were conducted at 0 (T1), 0.5 (T2) and 3 d (T3) after Fe-deficiency stress, and the timepoints were determined with a preliminary physiological experiment. In all, 6907, 5328, and 3593 differentially expressed genes (DEGs) were identified in pairs of T2 vs. T1, T3 vs. T1, and T3 vs. T2. Several of the enriched DEGs were related to heme binding, Fe ion binding, thylakoid membranes, photosystem II, photosynthesis-antenna protein, porphyrin and chlorophyll metabolism and carotenoid biosynthesis under Fe deficiency, which suggests that Fe deficiency mainly affects the photosynthesis of M. halliana. Additionally, we found that Fe deficiency induced significant down-regulation in genes involved in photosynthesis at T2 when seedlings were treated with Fe-deficient solution for 0.5 d, indicating that there was a rapid response of M. halliana to Fe deficiency. A strong up-regulation of photosynthesis genes was detected at T3, which suggested that M. halliana was able to recover photosynthesis after prolonged Fe starvation. A similar expression pattern was found in pigment regulation, including genes for coding chlorophyllide a oxygenase (CAO), β-carotene hydroxylase (β-OHase), zeaxanthin epoxidase (ZEP) and 9-cis-epoxycarotenoid dioxygenase (NCED). Our results suggest that pigment regulation plays an important role in the Fe deficiency response. In addition, we verified sixteen genes related to photosynthesis-antenna protein, porphyrin and chlorophyll metabolism and carotenoid biosynthesis pathways using quantitative real-time PCR (qRT-PCR) to ensure the accuracy of transcriptome data. Photosynthetic parameters, Chl fluorescence parameters and the activity of Chlase were also determined.ConclusionsThis study broadly characterizes a molecular mechanism in which pigment and photosynthesis-related regulations play indispensable roles in the response of M. halliana to short-term Fe deficiency and provides a basis for future analyses of the key genes involved in the tolerance of Fe deficiency.
Highlights
Iron (Fe) is an essential micronutrient for plants
Photosynthesis is driven by photosystem I (PSI) and photosystem II (PSII), which are two multisubunit complexes that are embedded in the thylakoid membrane of plants [8, 9]
LHCII is a trimer of any combination of the three complexes Lhcb1 to 3 with a high degree of similarity, yet the minor antenna consists of the three monomers from Lhcb4 to 6
Summary
Iron (Fe) is an essential micronutrient for plants. Utilization of Fe deficiency-tolerant rootstock is an effective strategy to prevent Fe deficiency problems in fruit trees production. Fe deficiency in photosynthetic organisms does lead to chlorosis but it is accompanied by the inhibition of photosynthetic electron transport reactions and by a loss of photosynthetic components and other adverse effects on photosynthesis [6, 7]. LHCs in plants contain the same pigments, including Chl-a and b molecules as well as a small number of carotenoids associated with the LHCs family of proteins [10, 11]. Two minor LHCI-like proteins (Lhca and 6) that have a high degree of similarity to Lhca to 4 were identified in Arabidopsis [10]. LHCII is a trimer of any combination of the three complexes Lhcb to 3 with a high degree of similarity, yet the minor antenna consists of the three monomers from Lhcb to 6. Lhcb to 6 are exclusively associated with PS II and Lhcb and 2 form mixed trimers that can be associated with either photosystem
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