Transcriptome Changes Associated with Boron Deficiency in Leaves of Two Citrus Scion-Rootstock Combinations.

Xiao Liu,Ling-Xia Guo,Long-Fei Jin,Zhao Deng,Yong-Zhong Liu,Wei Du,Shu-Ang Peng,Jia-Wei Zhang,Syed B Hussain

doi:10.3389/fpls.2017.00317

Abstract

Boron (B) deficiency stress is frequently observed in citrus orchards and causes considerable loss of productivity and fruit quality. Carrizo citrange (Cc) has been reported as a rootstock more tolerant to B deficiency than Trifoliate orange (To). The ‘Newhall’ navel orange (Ns) performed better when grafted onto Cc (Ns/Cc) than when grafted onto To (Ns/To) under long-term B deficiency. The present study confirmed that Ns/Cc had higher boron content, leaf fresh weight, lower leaf chlorosis and stronger photosynthesis ability than Ns/To. Moreover, B-deficiency significantly reduced the chlorophyll and carotenoid content in Ns/To. The content of total soluble sugar and lignin were dramatically increased and the expression levels of photosynthesis-related genes were substantially down-regulated in Ns/To by B-deficient treatment. B-deficiency also strongly induced expression levels of chlorophyll decomposition-related genes, glucose synthesis-related genes and lignin synthesis-related genes, and significantly inhibited the expression of carotenoid synthesis-related genes in Ns/To. Overall, these findings suggested that the influence of To on the scion of Ns was worse than that of Cc due to differently regulating these metabolic pathways under the long term of B-deficiency. The transcriptome analysis provided further information for understanding the mechanism of the different responses of scion-rootstock combinations to B-deficiency stress.

Highlights

Boron (B) plays important roles in numerous metabolic and physiological processes of higher plants, including sugar transport, cell wall synthesis and lignification, cell wall structure maintenance, carbohydrate metabolism, RNA metabolism, respiration, indole acetic acid metabolism, phenol metabolism, and membrane transport (Blevins and Lukaszewski, 1998; Brown et al, 2002; Bolaños et al, 2004; Marschner, 2012)
Previous studies found that the scion leaf growth, boron content and photosynthetic parameters in Ns/Carrizo citrange (Cc) were less affected by low B treatments than those in Ns/Trifoliate orange (To) (Sheng et al, 2010; Wang et al, 2014)
The results showed that Ns grafted onto Cc (Ns/Cc) had better leaf fresh weight, boron content and photosynthetic parameters than Ns grafted onto To (Ns/To) (Figures 1, 4) during long-term B-deficient treatment

Summary

Introduction

Boron (B) plays important roles in numerous metabolic and physiological processes of higher plants, including sugar transport, cell wall synthesis and lignification, cell wall structure maintenance, carbohydrate metabolism, RNA metabolism, respiration, indole acetic acid metabolism, phenol metabolism, and membrane transport (Blevins and Lukaszewski, 1998; Brown et al, 2002; Bolaños et al, 2004; Marschner, 2012). Geng et al (2003) revealed that cotton cultivars tolerant to B. Transcriptome Changes of Grafted Citrus deficiency had greater uptake rates and improved B utilization compared with cultivar sensitive to B deficiency. The seedling height and the rapeseed quality of B-efficient plants were slightly affected by B deficiency stress compared with that of B-inefficient plants (Geng et al, 1998). Comparison of seven citrus rootstocks under B-deficient conditions showed that Carrizo citrange (Cc) was the most tolerant genotype while Trifoliate orange (To) was the most sensitive genotype, according to the parameters of dry mass, leaf area, seedling height and the content of mineral nutrients (Zhou et al, 2013)

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