AtGASA4在紅外光訊息傳遞中之功能性研究

Abstract

先前由差異表現法處理3-5 μm波長紅外光之綠豆中篩選到受誘導之基因VrGIR1 (gibberellic acid[GA]-and infrared[IR]-induced gene1)，以及在阿拉伯芥中的相似基因GASA4 (gibberellic acid-stimulated transcripts in Arabidopsis) 在不同光源下表現量均不同，但GASA4在紅外光的訊息傳遞當中並不甚了解其所扮演的功能。論文中利用GASA4做為指標基因，發現它突變之後在紅外光處理下下胚軸的長度較野生型長，表示GASA4突變之後對紅外光較為不敏感；而大量表現GASA4基因也可得到較野生型更為短的下胚軸；以GASA4的啟動子表現GASA4轉入野生型及gasa4突變體中的轉殖株亦在紅外光照射下有相較於其背景植物較短的下胚軸。但是在基因表現層次方面卻發現突變株的CHS基因表現量在處理紅外光後較野生型表現量高，而相對應的生理表型花青素的累積也較野生型高出許多。利用GASA4基因自身的啟動子表現綠螢光蛋白(GFP)接GASA4的質體送入原生質體 (protoplast)後，無論是不同光源照射下或施加不同的賀爾蒙後綠螢光訊號分布的位置皆有所不同，顯示GASA4的確會受光源及賀爾蒙而影響表現。更進一步進行微陣列生物晶片的分析，發現紅外光的照射能誘導PSAK (or PSIK, photosystem I subunit K)基因及NPQ4 (nonphotochemical quenching 4)基因的顯著表現，暗示紅外光可藉由改變光系統反應中心的構型影響光合作用的效率，進一步調控植物的生長發育。而且NPQ4基因的表現量在gasa4突變株亦較照射紅外光之野生型高出許多，顯示在紅外光持續照射下，若缺少GASA4基因的存在，植物會將紅外光的能量視為過多的光通量而進行非光化學能消散的能量排除，而達到維持植物正常生長發育的效果。

The effects of visible light on photomorphogenesis have been extensively studied and its triggered signal transductions have been well recognized in plants. Unlike these light sources, infrared (IR) light is invisible and has been widely used in national defense industry and medical treatments. In previous study, gibberellic acid[GA]-and IR-induced gene1 (VrGIR1) was isolated by differential display from mungbean (Vigina radiate) seedlings irradiated with 3~5 μm IR light. As its homolog in Arabidopsis, GASA4 (gibberellic acid-stimulated transcripts in Arabidopsis) was differentially ex-pressed under various light conditions. However, the function of GASA4 under IR re-mains unclear. Thus, my thesis mainly investigates possible functions of GASA4 in IR signaling pathway. Here, we utilize molecular and genetic approaches to elucidate hy-pocotyl lengths of Arabidopsis seedlings under IR treatment, and to understand whether gasa4 is involved in IR signaling. The gasa4 mutant showed a longer hypocotyl than wild type under IR treatment, whereas over-expression lines of GASA4 exhibited a shorter hypocotyl than wild type. Furthermore, we introduced the GASA4 promot-er-driven GFP-GASA4 fusion construct into wild type and gasa4. Those transgenetic seedlings showed a shorter hypocotyl than their genetic-background control under IR treatment. Gene expression data indicated that light responsive genes such as CHS and RbcS1a, were upregulated in gasa4 mutant under IR treatment. In addition, higher an-thocyanin accumulation was observed in gasa4. Taken together, these results indicated that AtGASA4 may be a positive regulator in IR signaling. Moreover, Microarray Analy-sis revealed that PSAK (or PSIK, photosystem I subunit K) and NPQ4 (nonphotochem-ical quenching 4) are induced by IR treatment. Thus, our data imply that IR may change the structure of photosystem to modulate the photosystem efficiency, and then affect plant growth and development.