The Response Of Arabinoglactan-proteins (AGPs) In Banana (Musa Spp.) To Low Temperature Stress

Banana(Musa spp.) is the world’s most important tropical and subtropical fruits and crops. Banana production in our country is often sufferred from chilling injury. Plant chilling injury refers to the damages in chilling-sensitive plants when exposured to the low temperature which is above 0℃(usually refers to 0-15℃). Plant cell walls are the first line of defense when encountered stresses. Many studies have shown that hydroxyproline-rich glycoproteins(HRGPs), as a structural protein of plant cell walls, play an important role in plant cold acclimation mechanisms. However, as a very important member of HRGPs, very few studies are invoved in the function of arabinoglactan-proteins(AGPs) in the resistance of plant to low temperature.In the present study, digital gene expression techniques and qPCR were used to study the responses of AGPs in banana to low temperature stresses at transcritp level, using chilling-sensitive cultivar ’Baxijiao’(Musa spp. AAA cv. Baxijiao) and chilling-tolerant cultivar ’Dongguandajiao’(Musa spp. ABB cv. Dongguandajiao) as plant materials. In additional, 9 types of monoclonal antibodies recognizing AGPs were employed to study the distribution and different expression of their antigens in banana under cold wave using immunofluorescence labelling. Furthermore, the relative conductivity, relative water content, blade injury rate in banana under chilling stresses were measured. The goal of this study is to reveal the changes of AGPs in banana under low temperature stresses and enrich the mechanism of chilling resistance. The main results obtained are as follows:1. Physiological levels: the relative conductivity and leaf damage percentage of’Baxijiao’ were higher than those of ’Dongguandajiao’ under low temperatue. On the other hand, the relative water content of ’Dongguandajiao’ was higher than that of ’Baxijiao ’.2. Transcript level:(1) DGE results showed that 21 AGP members in banana showed differentiallyexpressed after low temperature treatment. Of which, 8 AGPs showed relatively high expression. As the temperature decreases from 25 ℃ to 10 ℃, the RPKM values of these 8AGPs increased.(2) qPCR results showed the transcript levels of all 8 AGPs except in Ma FLA2-2 in the chilling-tolerant cultivar decreased with the increase of the air temperature during cold wave. However, except for Ma FLA6 other levels in the chilling-sensitive cultivar increased.Artificial low temperatue stress resulted in accumulation of Ma FLA2-1, Ma FLA2-2,Ma FLA8 and Ma FLA20 while the level of Ma FLA2-2 in ‘Baxijiao’ was just on the opposite.3 Protein levels:(1) The antigens of different antibodies showed differential distribution and levels in banana under cold wave. With the decrease of the temperature, the AGP epitopes recognized by JIM8, JIM15, JIM14, PN16.4B and LM14 antibodies showed similar trends in the ’Baxijiao’ and ’Dongguandajiao’. On the other hand the antigen levels of CCRC-M32 and JIM16 antibodies showed contradict trends in both banana cultivars. At 7℃, the AGP levels recognized by CCRC-M32, JIM16, PN16.4B and LM2 antibodies ’Baxijiao’ were higher than those in ’Dongguandajiao’.(2) The antigen of rG25500 antibody reached the top at 16 ℃. Meanwhile, as the temperature continues to decrease, ’Baxijiao’ leaves such polyclonal antibodies identified AGPs levels have decreased.