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

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.

Transcriptome Analysis Reveals the Different Response to Toxic Stress in Rootstock Grafted and Non-Grafted Cucumber Seedlings

“…However, no significant difference of chlorophyll a, b and a + b was found in rootstock grafted cucumber compared to control. The result indicated grafting onto figleaf gourd regulated the reduction of Chl accumulation in cucumber leaves, which are consistent with the results obtained by [30]. Furthermore, the transcriptome data showed that the expression levels of Chl synthesis-related genes were significantly down-regulated in NG while they were not or slightly down-regulated in RG cucumber when compared to respective control (Table S10).…”

“…However, after grafted onto figleaf gourd, photosynthetic parameters of cucumber leaf, with the exception of Gs, exhibited steady state. A similar report of grafting triggering stronger photosynthetic ability was found in citrus under abiotic stress [30]. All of 14 DEGs encoded chlorophyll a-b binding protein were down-regulated in NG while two of them were down-regulated in RG, and the rate of descent was lower in RG than NG (Table S10).…”

Lignin Accumulation in Three Pumelo Cultivars in Association with Sucrose and Energy Depletion

“…It was shown that, lignin accumulated when sugar was in rapid decrease in the peach endocarp, indicating that lignin accumulation was in association with the declined sugar content, which accelerated the pit hardening process [26]. Other studies showed that total soluble sugar content increased significantly as well as lignin, and genes related to glucose and lignin synthesis were strongly induced by boron deficiency stress in leaves of citrus [27]. The possible link between lignin accumulation with sugar metabolism was reinforced by the observation that sugars availability positively affected the cell wall biosynthesis, which included lignin synthesis in Arabidopsis thaliana [28].…”

Boron Deficiency Increases Cytosolic Ca2+ Levels Mainly via Ca2+ Influx from the Apoplast in Arabidopsis thaliana Roots

“…Nevertheless, the main function of this micronutrient is its structural role in the cell wall where borate forms a diester bond between apiose residues of two rhamnogalacturonan II monomers, providing an enhanced firmness to the cell wall [19,20]. Moreover, B deprivation does not only affect the cell wall but also disturbs many metabolic and physiological processes such as membrane and cytoskeleton structure and function, oxidative stress and secondary metabolism, nitrogen assimilation, and gene expressions, among others [14,18,21,22,23,24,25,26,27,28].…”