Abstract
Boron (B) deficiency has seriously negative effect on citrus production. Carrizo citrange (CC) has been reported as a B-deficiency tolerant rootstock. However, the molecular mechanism of its B-deficiency tolerance remained not well-explored. To understand the molecular basis of citrus rootstock to B-deficiency, suppression subtractive hybridization (SSH) and microarray approaches were combined to identify the potential important or novel genes responsive to B-deficiency. Firstly four SSH libraries were constructed for the root tissue of two citrus rootstocks CC and Trifoliate orange (TO) to compare B-deficiency treated and non-treated plants. Then 7680 clones from these SSH libraries were used to construct a cDNA array and microarray analysis was carried out to verify the expression changes of these clones upon B-deficiency treatment at various time points compared to the corresponding controls. A total of 139 unigenes that were differentially expressed upon B-deficiency stress either in CC or TO were identified from microarray analysis, some of these genes have not previously been reported to be associated with B-deficiency stress. In this work, several genes involved in cell wall metabolism and transmembrane transport were identified to be highly regulated under B-deficiency stress, and a total of 23 metabolic pathways were affected by B-deficiency, especially the lignin biosynthesis pathway, nitrogen metabolism, and glycolytic pathway. All these results indicated that CC was more tolerant than TO to B-deficiency stress. The B-deficiency responsive genes identified in this study could provide further information for understanding the mechanisms of B-deficiency tolerance in citrus.
Highlights
Abiotic stress, such as nutrient deficiency or toxicity, drought, high salinity, extreme temperature, and flooding is a major cause of crop loss worldwide, reducing average yields for most major crop plants by more than 50% (Bray et al, 2000)
Vein swelling or cracking was observed in the leaves of Trifoliate orange (TO) under B-deficiency conditions, whereas no significant visual symptoms were detected in Carrizo citrange (CC), except for a slight yellowing found in several leaves at the end of the experiment (Figures 1E,F)
The lateral roots of TO were longer under normal conditions, but they were shorter and thicker under B-deficiency conditions (Figure 1B); no significant difference was found in CC (Figure 1A)
Summary
Abiotic stress, such as nutrient deficiency or toxicity, drought, high salinity, extreme temperature, and flooding is a major cause of crop loss worldwide, reducing average yields for most major crop plants by more than 50% (Bray et al, 2000). It is well-known that boron (B) is an essential micronutrient required for plant growth and development, which affects yield and the quality of crops (Warington, 1923; Brown et al, 2002). Previous physiological studies on the effects of B-deficiency to the root elongation (Kouchi and Kumazawa, 1975), leaf expansion (Dell and Huang, 1997), viable pollen grain production, and pollen tube elongation (Cheng and Rerkasem, 1993) were conducted
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