Genome-Wide Survey Reveals Transcriptional Differences Underlying the Contrasting Trichome Phenotypes of Two Sister Desert Poplars.

Jianchao Ma,Xiaotao Bai,Xiaodong He,Dongshi Wan,Zhimin Niu,Ningning Chen,Bingbing Duan,Xuemin Shao

doi:10.3390/genes7120111

Abstract

Trichomes, which are widely used as an important diagnostic characteristic in plant species delimitation, play important roles in plant defense and adaptation to adverse environments. In this study, we used two sister poplar species, Populus pruinosa and Populus euphratica—which have, respectively, dense and sparse trichomes—to examine the genetic differences associated with these contrasting phenotypes. The results showed that 42 and 45 genes could be identified as candidate genes related to trichomes in P. pruinosa and P. euphratica, respectively; most of these genes possessed high degrees of diversification in their coding sequences, but they were similar in intron/exon structure in the two species. We also found that most of the candidate trichome genes were expressed at higher levels in P. pruinosa, which has dense trichomes, than in P. euphratica, where there are few trichomes. Based on analyses of transcriptional profiles, a total of 195 genes, including many transcription factors, were found to show distinct differences in expression. The results of gene function annotation suggested that the genes identified as having contrasting levels of expression level are mainly associated with trichome elongation, ATPase activity, and hormone transduction. Changes in the expression of these and other related genes with high sequence diversification may have contributed to the contrast in the pattern of trichome phenotypes between the two species.

Highlights

The trichome, an important phenotypic characteristic found widely in unrelated plants, is used in the delimitation and identification of plant species [1,2]
Differences in leaf shape while in P. euphratica seedlings, lanceolate leaves may be more suited to preventing insect attack and and trichome pattern may work together to assist P. euphratica and P. pruinosa in adapting reducing evapotranspiration
The results indicated that most trichome candidate gene pairs began to differentiate about one million years ago (Mya), which is largely consistent with previous estimates of the divergence time of these two species [32,35,36], suggesting that most trichome candidate genes began to diversify following the divergence of the two species and that some mutant sites became fixed in the genome, which could have contributed to adaptations to diverse environments, such as the production of dense trichomes in seedling leaves of P. pruinosa

Summary

Introduction

The trichome, an important phenotypic characteristic found widely in unrelated plants, is used in the delimitation and identification of plant species [1,2]. Trichomes are enlarged and modified epidermal cells that grow perpendicular to the plant surface; they are produced by specialized processes of cellular differentiation, development, and repatterning [3,5]. It has been suggested that the formation of trichomes associated with the processes of plant development and adaptation of plants to various environments is regulated by complex networks in which both endogenous and environmental signals are involved [6,7,8]. Multiple lines of evidence from the model plant Arabidopsis suggest that three major groups of transcription factors (TFs) are involved in regulating the development of trichomes and their spatial and temporal distribution. Several genes of the basic helix-loop-helix (bHLH) family, such as

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