許多植物為了適應周圍環境，發展出了不同的運動方式，其中可以簡單分為快速的觸發運動 (seismonastic movement) 以及緩慢的睡眠運動 (nyctinastic movement) 。豆科的含羞草屬 (Mimosa) 是一個同時擁有這兩種運動能力的典型植物，其運動器官—葉枕藉由改變伸細胞 (extensor cells) 以及屈細胞 (flexor cells) 的體積驅使葉片運動。由於含羞草屬物種間具有快速運動能力之差異，顯示其基因體差異必然藏有調控觸發運動速率的演化足跡。因此，本研究利用比較基因體分析探討含羞草 (M. pudica) 、刺軸含羞木 (M. pigra) 、美洲含羞草 (M. diplotricha) 以及 M. casta 這四種具有不同運動速率之物種的葉枕表現基因，試著找出物種間序列變異與快速運動差異之關聯性；並利用與阿拉伯芥與五個豆科物種之已發表基因體資料作比較，以檢驗基因體中受到正向天擇影響的基因。本研究結果支持葉片運動速率較快的 M. pudica 與 M. casta 之親緣關係較相近。相對於與其他植物類群共有的基因群，含羞草屬特有的同源基因顯現最高的同義置換率，可能歸因於這些基因來自近代基因複製，較不受天擇壓力所影響。有趣的是，這群基因中為正向天擇基因的比例也最高 (36%) ，顯示這些基因可能發展出新功能 (neofunctionalization) 影響，例如在具觸發運動能力之葉枕中大量表現的機械式離子通道 MSL10 之同源基因。 此外， GO (gene ontology) 分析結果顯示含羞草屬特有同源基因中的正向天擇基因有許多與運動相關之基因，如 VDCA1 。綜合以上結果，本研究推測含羞草屬分支出現後演化出之基因可能為影響快速運動之重要指標，未來將進一步利用基因剔除方式驗證這些基因是否真正參與在含羞草屬快速運動。

Some plants perform seismonastic (rapid) or nyctinastic (slow) movements. Mimosa is a classic genus that has both abilities. The rapid movement of Mimosa is driven by pulvinus with asymmetrical volume changes of flexor and extensor motor cells. Mimosa has more than 500 species showing different seismonastic motility. However, little is known on the genetic variations associated with the evolution of rapid movement. Hence, we conducted comparative transcriptomics on the pulvini of four Mimosa species, M. pudica, M. diplotricha, M. pigra, and M. casta, which display different leaf sensitivity to touching. Additionally, Arabidopsis thaliana and five legumes with published genome information were included. The phylogenetic tree reconstructed by pulvinus-expressed genes supported the sister relationship between M. pudica and M. casta. In addition, we found the orthologous genes shared only by Mimosa species (‘Mimosa’) have higher synonymous substitution rate, probably due to relaxed selections on recently duplicated genes. Nevertheless, the ‘Mimosa’ group revealed the highest proportion of positively selected genes. The results suggested that these duplicated genes served as a likely target for neofunctionalization, particularly a gene homologous to mechanosensitive anion channel MSL10. The MSL10 homolog also showed drastic increase of the expression level in seismonastic pulvini. GO analysis indicated some positively selected genes of ‘Mimosa’ were enriched in movement-related functions, such as VDAC1. In conclusion, our analyses suggested the genes evolved after the emergence of Mimosa lineage are likely to play important roles in the innovation of rapid movement. In the future, corresponding knockout mutants will be generated to prove the expectation.

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