Identification of Sieve Element Occlusion Gene (SEOs) Family in Rubber Trees (Hevea brasiliensis Muell. Arg.) Provides Insights to the Mechanism of Laticifer Plugging

Xuan Wang,Linlin Cheng,Guishui Xie,Zifan Liu,Wentao Peng,Feng An

doi:10.3390/f13030433

Abstract

P proteins encoded by SEOs (sieve element occlusion) have been shown to be associated with the blockage of sieve tubes after injury in many plants, but the presence of SEO genes and their association with rubber tree laticifer plugging and latex yield remain unclear. Through a systematic identification and analysis, seven SEO genes were identified from the rubber tree genome. The physicochemical properties of their proteins, gene structures, conserved domains, and locations on chromosomes were analyzed. According to their phylogenetic distance, HbSEOs were divided into two clusters. The transcript levels of HbSEO genes varied with tissues, in which HbSEO3 and HbSEO4 were most highly expressed in leaf, bark, and latex. HbSEOs could be induced by ethephon, methyl jasmonate, mechanical injury, and tapping; furthermore, they were highly expressed in trees with short flow duration, suggesting their possible association with rubber tree laticifer plugging and latex yield. To our knowledge, this is the first report of HbSEOs in rubber trees. It provides us with a better understanding of the mechanism of laticifer plugging.

Highlights

Natural rubber is an important industrial raw material, which comes from the cytoplasm flow of rubber tree phloem after periodic tapping [1,2]
Both latex flow duration and flow velocity are relevant to laticifer plugging, since laticifer plugging after tapping forms gradually, resulting in the slowing down and eventually total stoppage of the latex flow [4]
Using published SEO sequences of A. thaliana, P. trichocarpa, and R. communis as queries, a total of 24 rubber tree putative SEO proteins were obtained by local BLASTP

Summary

Introduction

Natural rubber is an important industrial raw material, which comes from the cytoplasm flow of rubber tree phloem after periodic tapping [1,2]. The rubber tree latex yield after each tapping of rubber trees is determined by latex flow velocity and flow duration [3]. Both latex flow duration and flow velocity are relevant to laticifer plugging, since laticifer plugging after tapping forms gradually, resulting in the slowing down and eventually total stoppage of the latex flow [4]. The formation of laticifer blockage at the tapping cut of rubber trees has been confirmed by both repeated tapping and bark anatomy observation [5]. Many hypotheses have been suggested to explain the mechanism.

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Conclusion