Foster Toshi M, McAtee Peter A, Waite Chethi N, Boldingh Helen L, McGhie Tony K
The New Zealand Institute for Plant and Food Research Limited, Palmerston North 4474, New Zealand.
The New Zealand Institute for Plant and Food Research Limited, Auckland 1142, New Zealand.
Hortic Res. 2017 Apr 5;4:17009. doi: 10.1038/hortres.2017.9. eCollection 2017.
Apple dwarfing rootstocks cause earlier shoot termination and reduced root and shoot mass. To identify physiological factors responsible for rootstock-induced growth restriction, we compared vascular-enriched gene expression between two dwarfing rootstocks ('M27' and 'M9') and the vigorous rootstock 'M793' using RNA sequencing and quantitative reverse transcriptase PCR. Differentially expressed genes common to both dwarfing rootstocks belonged to five main biological processes: (1) primary metabolism, (2) cell wall synthesis and modification, (3) secondary metabolism, (4) hormone signalling and response and (5) redox homeostasis. Genes promoting the biosynthesis of amino acids, lipids and cell walls were downregulated in dwarfing rootstocks, whereas genes promoting the breakdown of these compounds were upregulated. The only exception to this trend was the upregulation of starch synthesis genes in dwarfing rootstocks. Non-structural carbohydrate analysis demonstrated that starch concentrations in 'M9' roots, stems and grafted 'Royal Gala' ('RG') scions were double that of equivalent tissues from 'RG' homo-grafted trees ('RG'/'RG'). Fructose and glucose concentrations were much lower in all three tissues of the 'RG'/'M9' trees. Together, these data indicate that dwarfing rootstocks are in a state of sugar depletion and reduced cellular activity despite having large starch reserves. Another significant finding was the over-accumulation of flavonoids and the downregulation of auxin influx transporters MdAUX1 and MdLAX2 in dwarfing rootstocks. We propose that both factors reduce polar auxin transport. The results of this study contribute novel information about the physiological state of dwarfing rootstocks.
苹果矮化砧木会导致新梢提前停止生长，并减少根和地上部的质量。为了确定导致砧木诱导生长受限的生理因素，我们使用RNA测序和定量逆转录PCR，比较了两种矮化砧木（“M27”和“M9”）与乔化砧木“M793”之间维管束富集基因的表达情况。两种矮化砧木共有的差异表达基因属于五个主要生物学过程：（1）初级代谢，（2）细胞壁合成与修饰，（3）次级代谢，（4）激素信号传导与响应，以及（5）氧化还原稳态。促进氨基酸、脂质和细胞壁生物合成的基因在矮化砧木中下调，而促进这些化合物分解的基因则上调。这种趋势的唯一例外是矮化砧木中淀粉合成基因的上调。非结构性碳水化合物分析表明，“M9”根、茎和嫁接的“皇家嘎啦”（“RG”）接穗中的淀粉浓度是“RG”自嫁接树（“RG”/“RG”）同等组织的两倍。“RG”/“M9”树的所有三种组织中的果糖和葡萄糖浓度要低得多。综合这些数据表明，矮化砧木尽管有大量淀粉储备，但处于糖耗尽和细胞活性降低的状态。另一个重要发现是矮化砧木中黄酮类化合物的过度积累以及生长素内流转运蛋白MdAUX1和MdLAX2的下调。我们认为这两个因素都会降低生长素的极性运输。本研究结果为矮化砧木的生理状态提供了新的信息。
