PNAS∣中國農業大學發文揭示玉米高緯度適應性機理

2017年12月26日PNAS在線文章，本文為中國農業大學，國家玉米改良中心田豐教授課題組發表，文章揭示了具有轉座子活動豐富的玉米基因組，使玉米適應高緯度地區環境的機理。

原題目為：

ZmCCT9 enhances maize adaptation to higher latitudes

意義：

開花時間是作物適應當地環境的關鍵決定因素。作為自然和人工選擇的結果，玉米已經進化成為降低了光周期敏感性，適應美洲90°以上緯度地區。在這裡，我們展示了一個distant Harbinger-like轉座子，作為一個順式調控元件抑制ZmCCT9表達，以促進在高緯度長日照條件下的開花。ZmCCT9上的轉座子和第二個開花時間基因ZmCCT10上的另一功能性轉座子，在馴化後依次出現，並被選擇為玉米從熱帶向高緯度傳播的靶標。我們的研究結果表明，由轉座子插入產生的新的功能變異，幫助玉米迅速在廣泛的緯度範圍內傳播。

Significance：

Flowering time is a critical determinant of crop adaptation to local environments. As a result of natural and artificial selection, maize has evolved a reduced photoperiod sensitivity to adapt to regions over 90° of latitude in the Americas. Here we show that a distant Harbinger-like transposon acts as a cis-regulatory element to repress ZmCCT9 expression to promote flowering under the long days of higher latitudes. The transposon at ZmCCT9 and another functional transposon at a second flowering-time gene, ZmCCT10, arose sequentially following domestication and were targeted by selection as maize spread from the tropics to higher latitudes. Our results demonstrate that new functional variation created by transposon insertions helped maize to spread over a broad range of latitudes rapidly.

摘要：

從墨西哥西南部的熱帶起源，玉米已遍布在美洲的廣闊的緯度。這項壯舉，違背了作物禁止在緯度上輕易擴散的規則。玉米如何完成廣泛維度的適應，在很大程度上是未知的。通過定位克隆和關聯作圖，我們將一個開花時間的數量性狀基因座定位到CCT轉錄因子（ZmCCT9）上游57kb處的Harbinger-like轉座元件。長日照條件下，Harbinger-like轉座元件通過順式作用來抑制ZmCCT9表達，從而促進開花。通過CRISPR/Cas9敲除ZmCCT9，可在長日照條件下引起早開花。ZmCCT9受晝夜調節，負調控成花素ZCN8的表達，從而導致在長日照條件下的晚花。群體遺傳學分析表明，插入在ZmCCT9中的Harbinger-like轉座子，以及插入在另一個CCT旁系同源物，ZmCCT10中的CACTA-like轉座子，在馴化後依次出現，並被選擇為玉米從熱帶向高緯度傳播的靶標。我們的研究結果有助於解釋，在前哥倫布時代，具有轉座子活動豐富的動態玉米基因組是如何使玉米適應超過90°的緯度地區的。

Abstract：

From its tropical origin in southwestern Mexico, maize spread over a wide latitudinal cline in the Americas. This feat defies the rule that crops are inhibited from spreading easily across latitudes. How the widespread latitudinal adaptation of maize was accomplished is largely unknown. Through positional cloning and association mapping, we resolved a flowering-time quantitative trait locus to a Harbinger-like transposable element positioned 57 kb upstream of a CCT transcription factor (ZmCCT9). The Harbinger-like element acts in cis to repress ZmCCT9 expression to promote flowering under long days. Knockout of ZmCCT9 by CRISPR/Cas9 causes early flowering under long days. ZmCCT9 is diurnally regulated and negatively regulates the expression of the florigen ZCN8, thereby resulting in late flowering under long days. Population genetics analyses revealed that the Harbinger-like transposon insertion at ZmCCT9 and the CACTA-like transposon insertion at another CCT paralog, ZmCCT10, arose sequentially following domestication and were targeted by selection for maize adaptation to higher latitudes. Our findings help explain how the dynamic maize genome with abundant transposon activity enabled maize to adapt over 90° of latitude during the pre-Columbian era.

每日一詞

determinant

英[d??t?:m?n?nt]

美[d??t?:rm?n?nt]

n. 行列式; 決定因素; 決定物; 免疫因子;

adj. 決定因素的; 限定性的;

[例句]The windows and the views beyond them are major determinants of a rooms character.

窗戶和窗外的景色是決定一個房間特色的主要因素。

[其他] 複數：determinants