Expression and distribution of extensins and AGPs in susceptible and resistant banana cultivars in response to wounding and Fusarium oxysporum

Abstract

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is soil-borne disease of banana (Musa spp.) causing significant economic losses. Extensins and arabinogalactan proteins (AGPs) are cell wall components important for pathogen defence. Their significance for Foc resistance in banana was not reported so far. In this study, two banana cultivars differing in Foc sensitivity were used to monitor the changes in transcript levels, abundance and distribution of extensins and AGPs after wounding and Foc inoculation. Extensins mainly appeared in the root cap and meristematic cells. AGPs recognized by JIM13, JIM8, PN16.4B4 and CCRC-M134 antibodies located in root hairs, xylem and root cap. Individual AGPs and extensins showed specific radial distribution in banana roots. At the transcript level, seven extensins and 23 AGPs were differentially expressed between two banana cultivars before and after treatments. Two extensins and five AGPs responded to the treatments at the protein level. Most extensins and AGPs were up-regulated by wounding and pathogen inoculation of intact plants but down-regulated by pathogen attack of wounded plants. Main components responsible for the resistance of banana were MaELP-2 and MaPELP-2. Our data revealed that AGPs and extensins represent dynamic cell wall components involved in wounding and Foc resistance.

Figure 1

Immunolocalization of JIM11 (a–e) and JIM20 (f–j) epitopes in longitudinal and transversal sections of banana (Musa spp. AAA) roots. CC, cortical cells; DZ, differentiation zone; En, endodermis; Ep, epidermis; EZ, elongation zone; LRC, lateral root cap; LRP, lateral root primordium; M, meristem; Pe, pericycle; Pr, protoderm; QC, quiescent centre; RC, root cap; TZ, transition zone; VI, vascular initials; VC, vascular cylinder; Xy, xylem. Arrows point to tricellular cell–cell junction. Bars represent 100 μm (a,b,f,g) and 50 μm (c–e,h–j), respectively.

Figure 2

Immunolocalization of LM2 (a–d) and LM14 (e–h) epitopes in the cross and longitudinal sections of banana (Musa spp. AAA) roots. CC, cortical cells; DZ, differentiation zone; En, endodermis; Ep, epidermis; EZ, elongation zone; LRC, lateral root cap; M, meristem; Pe, pericycle; Pr, protoderm; QC, quiescent centre; RC, root cap; TZ, transition zone; VI, vascular initials; VC, vascular cylinder; Xy, xylem. Bars represent 100 μm (a,e–h) and 50 μm (b–d), respectively.

Figure 3. Immunolocalization of JIM16 epitope in the cross and longitudinal sections of banana (Musa spp. AAA) roots.

BLCs, border-like cells; CC, cortical cells; DZ, differentiation zone; En, endodermis; Ep, epidermis; EZ, elongation zone; LRC, lateral root cap; M, meristem; Ph, phloem; Pr, protoderm; QC, quiescent centre; RC, root cap; TZ, transition zone; VC, vascular cylinder; Xy, xylem. Bars represent 100 μm.

Figure 4

Immunolocalization of JIM13 (a–c), JIM8 (d,e), PN16.4B4 (f,g) and CCRC-M134 (h,i) epitopes in the cross and longitudinal sections of banana (Musa spp. AAA) roots. DZ, differentiation zone; Ep, epidermis; M, meristem; Pr, protoderm; RC, root cap; RH, root hairs; Xy, xylem. Bars represent 100 μm.

Figure 5

Changes in the transcript levels of extensin (a,b) and AGP (c) members in banana (Musa spp. AAA) roots after wounding and infection with Fusarium oxysporum f. sp. cubense. BX, Musa spp. AAA cv. Baxijiao (susceptible); YK, Musa spp. AAA cv. Yueyoukang 1 (resistant). AGP, arabinogalactan protein; C, control; W, wounding; I, inoculation of intact plants; WI, inoculation by pathogen after plant wounding. Values are the means ± SE (n = 3). More gene information is available at Supplementary Table S2.

Figure 6

Changes in the protein levels of extensins (a,b) and AGPs (c–g) in banana (Musa spp. AAA) roots after wounding and infection with Fusarium oxysporum f. sp. cubense. BX, Musa spp. AAA cv. Baxijiao (susceptible); YK, Musa spp. AAA cv. Yueyoukang 1 (resistant). AGPs, Arabinogalactan proteins; C, control; W, wounding; I, inoculation of intact plants; WI, inoculation by pathogen after plant wounding. The fluorescence density was calculated by ImageJ software. Values are the means ± SE (n = 3) and different letters indicate significant differences (one-way ANOVA, P < 0.05) between treatments.