初探高溫誘導番茄花序分枝

Abstract

全球氣候變遷下，提高番茄耐熱特性為目前重要的議題。本研究旨在探討高溫下番茄 (Solanum lycopersicum L.) 花序高度分枝之突變體heat-induced inflorescence (hin) 發生機制。hin突變株隨環境溫度從20°C漸進提高到35°C，花序分枝數量隨之增加；相對地，對照品種LA3120在不同溫度下仍維持單一聚繖花序。序列分析顯示，hin在兩個MADS-box轉錄因子JOINTLESS-2 (J2) 與ENHANCER OF JOINTLESS-2 (EJ2) 的非編碼區域具有變異，導致兩基因功能異常。LA3120 × hin的F2分離後代分析證實，j2TE/ej2w雙突變是高溫誘導花序分枝所必需的基因型。花/花序分生組織 (floral/inflorescence meristem, FIM) 之轉錄體分析顯示，兩基因型共享部分逆境反應基因，但hin在分生組織命運、荷爾蒙訊號與晝夜節律等途徑呈現特異性重編程。高溫下，花序分枝促進因子MULTIPLE INFLORESCENCE BRANCH 2 (MIB2) 及CONSTANS-LIKE 1 (COL1) 在hin中顯著上調；而FIM正向調控基因TM5、TM29、TAG1與ANANTHA等則下調，顯示J2/EJ2功能缺失導致分生組織穩定性喪失並啟動下游分枝路徑。綜合上述結果，本研究證明J2/EJ2功能喪失可驅動高溫下FIM的重編程並促進花序分枝，為理解番茄花序熱形態發生提供分子線索。

Enhancing heat tolerance in tomato has become an important issue under global climate change. This study aimed to investigate the molecular mechanism underlying the heat-induced inflorescence branching mutant (heat-induced inflorescence, hin) in tomato (Solanum lycopersicum L.). As the ambient temperature increased from 20 °C to 35 °C, the hin mutants exhibited a progressive increase in inflorescence branching; in contrast, the control cultivar LA3120 maintained a simple cymose inflorescence across all temperature conditions. Sequence analyses revealed that hin carries non-coding variants in two MADS-box transcription factors, JOINTLESS-2 (J2) and ENHANCER OF JOINTLESS-2 (EJ2), resulting in abnormal expression and function of both genes. Segregation analysis of the LA3120 × hin F2 population confirmed that the j2TE/ej2w double mutation is required for heat-induced inflorescence branching. Transcriptome profiling of the floral/inflorescence meristem (FIM) showed that although the two genotypes shared several stress-responsive genes, hin displayed genotype-specific transcriptional reprogramming in pathways related to meristem identity, hormonal signaling, and circadian regulation. Under high temperature, the branching-promoting factors MULTIPLE INFLORESCENCE BRANCH 2 (MIB2) and CONSTANS-LIKE 1 (COL1) were significantly upregulated in hin, whereas positive regulators of FIM maintenance, including TM5, TM29, TAG1, and ANANTHA, were downregulated. These results suggest that the loss of J2/EJ2 function disrupts meristem stability and activates downstream branching programs. Together, our results demonstrate that the loss of J2/EJ2 function drives the reprogramming of the FIM under high temperature and promotes inflorescence branching, providing molecular insights into inflorescence thermomorphogenesis in tomato.