Identification of ABC transporter G subfamily in white lupin and functional characterization of L.albABGC29 in phosphorus use

Abstract

Background: White lupin (Lupinus albus) is a leguminous crop with elite adaptive ability in phosphorus-deficient soil and used as a model plant for studying phosphorus (P) use. However, the genetic basis of its adaptation to low P (LP) remains unclear. ATPase binding cassette (ABC) transports G subfamily play a crucial role in the transportation of biological molecules across the membrane. To date, identification of this subfamily has been analyzed in some plants, but no systematic analysis of these transporters in phosphorus acquisition is available for white lupin.

Results: This study identified 66 ABCG gene family members in the white lupin genome using comprehensive approaches. Phylogenetic analysis of white lupin ABCG transporters revealed six subclades based on their counterparts in Arabidopsis, displaying distinct gene structure and motif distribution in each cluster. Influences of the whole genome duplication on the evolution of L.albABCGs were investigated in detail. Segmental duplications appear to be the major driving force for the expansion of ABCGs in white lupin. Analysis of the Ka/Ks ratios indicated that the paralogs of the L.albABCG subfamily members principally underwent purifying selection. However, it was found that L.albABCG29 was a result of both tandem and segmental duplications. Overexpression of L.albABCG29 in white lupin hairy root enhanced P accumulation in cluster root under LP and improved plant growth. Histochemical GUS staining indicated that L.albABCG29 expression increased under LP in white lupin roots. Further, overexpression of L.albABCG29 in rice significantly improved P use under combined soil drying and LP by improving root growth associated with increased rhizosheath formation.

Conclusion: Through systematic and comprehensive genome-wide bioinformatics analysis, including conserved domain, gene structures, chromosomal distribution, phylogenetic relationships, and gene duplication analysis, the L.albABCG subfamily was identified in white lupin, and L.albABCG29 characterized in detail. In summary, our results provide deep insight into the characterization of the L.albABCG subfamily and the role of L.albABCG29 in improving P use.

Keywords: ABCG subfamily; Duplication; Phosphorus; Rice; White lupin.

Fig. 1

Evolutionary relationship of the ABCG subfamily across different plant species. a An unrooted phylogenetic tree of ABCG proteins of L. albus, L. angustifolius, P. vulgaris, G. max, and A. thaliana. b Phylogenetic tree of white lupin ABCG subfamily genes only. The phylogenetic tree was constructed using IQ-TREE software under the LG + I + G model with ML ultrafast bootstrap value (1000). ABCG subfamily clustered into six groups (G-I to G-IV and G-VI) based on A. thaliana homologs in each group, represented by a different color arc

Fig. 2

Gene structure and evolutionary analysis of white lupin ABCG transporter subfamily. a Conserved domain analysis of ABCG genes. b Gene structural analysis of L.albABCG genes, 5′ to 3′ direction represent the orientation of nucleotide sequence and scale at the bottom represent the length of nucleotide (bp). c Conserved motif analysis of L.albABCG genes. d Predicted cis-regulatory elements of L.albABCG genes. Total 9 randomly distributed promoter cis-regulatory elements identified from 2 kb upstream region of each candidate gene. Each type of cis-regulatory element is represented with a different color box at the bottom. The final figure was colored and edited by using Adobe Illustrator CC software

Fig. 3

Gene duplication analysis of L.albABCG subfamily. a Synteny analysis of the white lupin ABCG subfamily revealed segmental duplication on different chromosomes. Different color lines indicate segmental duplication pairs of L.albABCG between chromosomes. b Collinearty map of only L.albABCG29 between G. max, L. angustifolius, and P. vulgaris. The Blue and green lines indicate L.albABCG29 syntenic block between G. max and L. albus chromosome 7/17 and chromosome 12, respectively. The red line indicates the syntenic block of L. albus L.albABCG29 with the corresponding chromosomes of L. angustifolius (chromosome 1, LG01) and blackline P. vulgaris (Chromosome 3, Chr_03)

Fig. 4

Tissue-specific expression pattern of selected L.albABCG genes under low P. in LR; lateral root, CR; cluster root was assessed. Four independent replicates were used to calculate expression in each tissue

Fig. 5

Phenotypic characterization of L.albABCG29 in white lupin grown under phosphorus sufficient (CK) and low phosphorus (LP) conditions. a Relative expression of L.albABCG29 in transgenic white lupin hairy roots b schematic representation of the GUS vectors for transient expression (top panel). The native promoter of L.albABCG29 drives GUS expression in transgenic L. albus roots under CK and LP conditions (lower panel), c phosphorus concentration (mg P g^− 1, DW) in different parts of white lupin root, d total root length (cm), e total plant biomass (g plant^− 1) of transgenic (OE-L1/L2) and wild type (WT) white lupin. Different letters show significant differences of mean ± SD of four replicates at P < 0.01 significance level. OE-L1, Overexpression Line 1; OE-L2, Overexpression Line 2

Fig. 6

Phenotype of L.albABCG29 overexpression in rice under combined water and phosphorus-deficient soil conditions. a Phenotypes of rice plant rizhosheath under SD + P and SD-P in both WT and L.albABCG29 overexpression lines, b relative expression level, c total root length (cm), d root hair length (mm), e specific rhizosheath weight (mg cm^− 1 root length), f phosphorus uptake efficiency in the shoot (mg P plant^− 1), g phosphorus uptake efficiency in the root (mg P plant^− 1), h rhizosheath P concentration (mg P g^− 1, DW). Different letters show significant differences of mean ± SD of four replicates at P < 0.01 significance level. SD + P; soil drying with phosphorus, SD-P; soil drying without phosphorus, WW + P; well-watered with phosphorus, WW-P; well-watered without phosphorus; OE-L1, Overexpression Line 1; OE-L2, Overexpression Line 2