Genome-Wide Identification of Aluminum-Activated Malate Transporter (ALMT) Gene Family in Rubber Trees (Hevea brasiliensis) Highlights Their Involvement in Aluminum Detoxification

Xiaowei Ma,Guishui Xie,Zifan Liu,Feng An,Dong Guo,Lifeng Wang

doi:10.3390/f11020142

Abstract

The rubber tree (Hevea brasiliensis) is a widely cultivated crop in tropical acidic soil that is tolerant to high concentration of aluminum and the aluminum-activated malate transporter (ALMT) plays an important role in plant aluminum detoxification. However, the effects of ALMT on rubber tree aluminum tolerance, growth performance, and latex production are unclear. In this study, 17 HbALMT genes were identified from the genome of rubber trees. The physiological and biochemical characteristics, phylogenetic relationships, gene structures, conserved motifs, cis-elements of promoter, and expression patterns of the identified HbALMT genes were studied. Phylogenetic relationships indicated that these genes were divided into four clusters and genes in the same cluster have similar gene structures and conserved motifs. The promoters of HbALMT genes contain many cis-elements associated with biotic stress and abiotic stress. Quantitative real-time PCR analysis revealed HbALMTs showed various expression patterns in different tissues, indicating the functional diversity of HbALMT genes in different tissues of rubber trees. Transcriptome analysis and qRT-PCR assay showed that most of the HbALMT genes responded to aluminum stress, and among the 17 HbALMTs, HbALMT1, HbALMT2, HbALMT13, and HbALMT15 displayed higher expression levels in roots after two or five days of Al treatments, indicating their potential involvement in aluminum detoxification. Taken together, this study laid a foundation for further understanding the molecular evolution of the ALMT genes and their involvement in rubber tree aluminum adaption.

Highlights

Soil acidification is a major stress that affects about 50% of potentially arable lands throughout the world, in tropical and subtropical zones [1,2]
A total of 17 members of the ALMT homologous genes were identified in the rubber tree genome by using BLAST and HMMER, which were named as HbALMT1-HbALMT17 according to the phylogenetic relationship with Arabidopsis
A total of 17 HbALMT genes were identified from the rubber tree genome

Summary

Introduction

Soil acidification is a major stress that affects about 50% of potentially arable lands throughout the world, in tropical and subtropical zones [1,2]. In the process of long-term evolution, many plant species in acidic soils have developed a series of tolerance mechanisms to cope with and resist Al toxicity [7]. Gramineous plants, such as maize and wheat, show signs of inhibiting root growth within minutes or hours of being exposed to Al stress, even at micromolar concentration levels [3,8]. We found that rubber tree saplings could tolerate 100–200 mmol/L of Al at pH 4.2, which is far higher than other crops [13] Broader cultivation of these Al-resistant crops will help promote the development of sustainable agriculture. The underlying mechanism, especially the molecular mechanism of plant Al tolerance, is still unclear

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Results

Discussion

Conclusion