De novo Transcriptome Analysis Reveals Distinct Defense Mechanisms by Young and Mature Leaves of Hevea brasiliensis (Para Rubber Tree).

Yongjun Fang,Chaorong Tang,Xiaohu Xiao,Meng Yang,Xiangyu Long,Songnian Hu,Binhui Zhou,Yacheng Huang,Hailiang Mei

doi:10.1038/srep33151

Abstract

Along with changes in morphology in the course of maturation, leaves of Hevea brasiliensis become more resistant to leaf diseases, including the South American Leaf Blight (SALB), a devastating fungal disease of this economically important tree species. To understand the underlying mechanisms of this defense, and to identify the candidate genes involved, we sequenced the Hevea leaf transcriptome at four developmental stages (I to IV) by Illumina sequencing. A total of 62.6 million high-quality reads were generated, and assembled into 98,796 unique transcripts. We identified 3,905 differentially expressed genes implicated in leaf development, 67.8% (2,651) of which were during the transition to leaf maturation. The genes involved in cyanogenic metabolism, lignin and anthocyanin biosynthesis were noteworthy for their distinct patterns of expression between developing leaves (stages I to III) and mature leaves (stage IV), and the correlation with the change in resistance to SALB and the Oidium/Colletotrichum leaf fall. The results provide a first profile of the molecular events that relate to the dynamics of leaf morphology and defense strategies during Hevea leaf development. This dataset is beneficial to devising strategies to engineer resistance to leaf diseases as well as other in-depth studies in Hevea tree.

Highlights

In stages of A, B and C are generally free of lignin and behave as nutrient sinks[4,5], whereas stage D leaves are source leaves with physiological and structural parameters of mature leaves
To generate the transcriptome of Hevea leaves, cDNA libraries were prepared from four representative stages of leaf development, i.e. bronze (I), colorchange (II), pale-green (III) and bright green (IV) (Fig. 1a), and subjected to paired-end sequencing (2 × 101 bp) using the Illumina HiSeq2000 platform
A series of candidate genes marking the developmental and defensive characteristics of expanding and mature leaves were found to be highly expressed at distinct leaf stages

Summary

Introduction

In stages of A, B and C are generally free of lignin and behave as nutrient sinks[4,5], whereas stage D leaves are source leaves with physiological and structural parameters of mature leaves. Hevea mature leaves (stage D) display a decreased cyanogenic ability, but structural hardening and lignin formation act to restrict fungal spread in the cell wall, resulting in complete resistance to SALB. It would appear that Hevea leaves undergo biochemical and structural changes, especially in the composition of secondary metabolites such as cyanogenic glucosides, anthocyanin, and lignin during the process of development. This contributes to the differing responses of young and mature leaves to biotic and abiotic stresses[1]. We sequenced the transcriptome of Hevea leaves in four developmental stages, and generated a panorama of transcriptome dynamics accompanying the leaf development. The data could serve as a foundation for a myriad of studies on this plant organ

Methods

Results

Conclusion