Miro Berta, Longkumer Toshisangba, Entila Frederickson D, Kohli Ajay, Ismail Abdelbagi M
Genetics and Biotechnology Division, International Rice Research Institute, Makati, Philippines.
Front Plant Sci. 2017 Oct 26;8:1857. doi: 10.3389/fpls.2017.01857. eCollection 2017.
The water-, energy-, and labor-intensive system of transplanted puddled rice () is steadily being replaced by direct seeding due to the progressive scarcity of these resources. However, the alternate dry direct seeding leads to competition with weeds and poor establishment when soils are flooded. Direct seeded rice capable of anaerobic germination (germination in flooded soil, AG) is ideal, which under rainfed ecosystems would also overcome waterlogging during germination. AG tolerance is associated with faster germination and faster elongation of coleoptiles, with the activities of alcoholic fermentation enzymes replacing aerobic respiration as a source of energy. To better understand the variability in the morpho-physiological responses and in the nature of the alcoholic fermentation enzymes during AG, 21 rice genotypes were studied. The genotypes Khao Hlan On (KHO) and IR42 were used as the tolerant and susceptible checks, respectively. KHO exhibited faster germination, with 82.5% of the coleoptiles emerging out of 10 cm of water within 8 days, whereas IR42 exhibited 20% germination and limited coleoptile growth. Among the test genotypes, four performed well, including two that are drought tolerant. Increased content and activity of the alcoholic fermentation enzymes, alcohol dehydrogenase (ADH1) and acetaldehyde dehydrogenase (ALDH2a and ALDH2b), was noted in KHO under anaerobic than under aerobic conditions and also in comparison with IR42 under AG. Gene transcripts for these enzymes were also more in KHO undergoing AG. However, no major differences were observed between KHO and IR42 in the critical -acting regulatory elements, such as the auxin, light, and sugar response elements, in the promoters of ADH1, ALDH2a, and ALDH2b genes. Post-transcriptional and post-translational regulatory mechanisms were implicated for the increased transcript and protein content/activity of the enzymes in KHO by observing four different transcripts of ALDH2a and a unique non-glycosylated form of ADH1 under AG. IR42 lacked the non-glycosylated ADH1 and contained only a truncated form of ALDH2a, which lacked the active site. Additionally, KHO exhibited increased activity and more isoforms for reactive oxygen species detoxifying enzymes under AG compared to IR42. These results highlight the need for a deeper functional understanding of the critical enzymes involved in AG.
由于水资源、能源和劳动力日益稀缺，移栽水稻的水、能源和劳动力密集型种植系统正逐渐被直播所取代。然而，交替旱直播会导致杂草竞争，且在土壤淹水时秧苗立苗情况不佳。具备厌氧发芽能力（在淹水土壤中发芽，即AG）的直播水稻是理想选择，在雨养生态系统中，它还能克服发芽期的涝害问题。AG耐受性与更快的发芽速度和更快的胚芽鞘伸长有关，此时酒精发酵酶的活性取代有氧呼吸成为能量来源。为了更好地了解AG过程中形态生理反应的变异性以及酒精发酵酶的性质，对21个水稻基因型进行了研究。基因型Khao Hlan On（KHO）和IR42分别用作耐受性和敏感性对照。KHO发芽更快，8天内82.5%的胚芽鞘从10厘米深的水中伸出，而IR42的发芽率为20%，胚芽鞘生长受限。在测试基因型中，有4个表现良好，其中包括2个耐旱基因型。与有氧条件相比，KHO在厌氧条件下以及与AG条件下的IR42相比，酒精发酵酶乙醇脱氢酶（ADH1）和乙醛脱氢酶（ALDH2a和ALDH2b）的含量和活性增加。在进行AG的KHO中，这些酶的基因转录本也更多。然而，在ADH1、ALDH2a和ALDH2b基因启动子中的关键作用调控元件，如生长素、光和糖反应元件方面，KHO和IR42之间未观察到重大差异。通过观察AG条件下ALDH2a的四种不同转录本和ADH1的一种独特非糖基化形式，推测KHO中酶的转录本和蛋白质含量/活性增加涉及转录后和翻译后调控机制。IR42缺乏非糖基化的ADH1，仅含有一种缺少活性位点的截短形式的ALDH2a。此外，与IR42相比，KHO在AG条件下活性氧解毒酶的活性增加且同工型更多。这些结果凸显了深入了解AG过程中关键酶功能的必要性。
