Sub1A

Function

Crop tolerance to flooding is an important agronomic trait. Although rice (Oryza sativa) is considered a flood tolerant crop, only limited cultivars display tolerance to prolonged submergence, which is largely attributed to the presence of the SUB1A gene.

Mechanisms

The Submergence Tolerance Regulator Sub1A Mediates Stress-Responsive Expression of AP2/ERF Transcription Factors 　　To elucidate the mechanism of Sub1A-1-mediated tolerance, we performed transcriptome analyses comparing the temporal submergence response of Sub1A-1-containing tolerant M202(Sub1) with the intolerant isoline M202 lacking this gene. We identified 898 genes displaying Sub1A-1-dependent regulation. Integration of the expression data with publicly available metabolic pathway data identified submergence tolerance-associated pathways governing anaerobic respiration, hormone responses, and antioxidant systems. Of particular interest were a set of APETALA2 (AP2)/ERF family transcriptional regulators that are associated with the Sub1A-1-mediated response upon submergence. Visualization of expression patterns of the AP2/ERF superfamily members in a phylogenetic context resolved 12 submergence-regulated AP2/ERFs into three putative functional groups: (1) anaerobic respiration and cytokinin-mediated delay in senescence via ethylene accumulation during submergence (three ERFs); (2) negative regulation of ethylene-dependent gene expression (five ERFs); and (3) negative regulation of gibberellin-mediated shoot elongation (four ERFs). These results confirm that the presence of Sub1A-1 impacts multiple pathways of response to submergence.

Regulatory interplay of the Sub1A and CIPK15 pathways in the regulation of α-amylase production in flooded rice plants 　　Rice (Oryza sativa L.) can successfully germinate and grow even when flooded. Rice varieties possessing the submergence 1A (Sub1A) gene display a distinct flooding-tolerant phenotype, associated with lower carbohydrate consumption and restriction of the fast-elongation phenotype typical of flooding-intolerant rice varieties. Calcineurin B-like interacting protein kinase 15 (CIPK15) was recently indicated as a key regulator of α-amylases under oxygen deprivation, linked to both rice germination and flooding tolerance in adult plants. It is still unknown whether the Sub1A- and CIPK15-mediated pathways act as complementary processes for rice survival under O2 deprivation. In adult plants Sub1A and CIPK15 may perhaps play an antagonistic role in terms of carbohydrate consumption, with Sub1A acting as a starch degradation repressor and CIPK15 as an activator. In this study, we analysed sugar metabolism in the stem of rice plants under water submergence by selecting cultivars with different traits associated with flooding survival. The relation between the Sub1A and the CIPK15 pathways was investigated. The results show that under O2 deprivation, the CIPK15 pathway is repressed in the tolerant, Sub1A-containing, FR13A variety. CIPK15 is likely to play a role in the up-regulation of Ramy3D in flooding-intolerant rice varieties that display fast elongation under flooding and that do not possess Sub1A.

The Submergence Tolerance Gene SUB1A Delays Leaf Senescence under Prolonged Darkness through Hormonal Regulation in Rice

   Leaf senescence is a natural age-dependent process that is induced prematurely by various environmental stresses. Typical alterations during leaf senescence include breakdown of chlorophyll, a shift to catabolism of energy reserves, and induction of senescence-associated genes, all of which can occur during submergence, drought, and constant darkness. Here, we evaluated the influence of the submergence tolerance regulator, SUBMERGENCE1A (SUB1A), in the acclimation responses during leaf senescence caused by prolonged darkness in rice (Oryza sativa). SUB1A messenger RNA was highly induced by prolonged darkness in a near-isogenic line containingSUB1A. Genotypes with conditional and ectopic overexpression of SUB1A significantly delayed loss of leaf color and enhanced recovery from dark stress. Physiological analysis revealed that SUB1A postpones dark-induced senescence through the maintenance of chlorophyll and carbohydrate reserves in photosynthetic tissue. This delay allowed leaves of SUB1A genotypes to recover photosynthetic activity more quickly upon reexposure to light. SUB1A also restricted the transcript accumulation of representative senescence-associated genes. Jasmonate and salicylic acid are positive regulators of leaf senescence, but ectopic overexpression of SUB1A dampened responsiveness to both hormones in the context of senescence. We found that ethylene accelerated senescence stimulated by darkness and jasmonate, although SUB1Asignificantly restrained dark-induced ethylene accumulation. Overall, SUB1A genotypes displayed altered responses to prolonged darkness by limiting ethylene production and responsiveness to jasmonate and salicylic acid, thereby dampening the breakdown of chlorophyll, carbohydrates, and the accumulation of senescence-associated messenger RNAs. A delay of leaf senescence conferred by SUB1A can contribute to the enhancement of tolerance to submergence, drought, and oxidative stress.

Labs working on this page

   Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California

　　Department of Crop Plant Biology, University of Pisa, Pisa, Italy 　　Plantlab, Scuola Superiore Sant’Anna, Pisa, Italy

References

1. Raj Kumar Niroula;Chiara Pucciariello;Viet The Ho;Giacomo Novi;Takeshi Fukao;Pierdomenico Perata

 SUB1A-dependent and -independent mechanisms are involved in the flooding tolerance of wild rice species
 The Plant Journal, 2012, 72(2): 282-293

2. Takeshi Fukao;Elaine Yeung;Julia Bailey-Serres

 The Submergence Tolerance Gene SUB1A Delays Leaf Senescence under Prolonged Darkness through Hormonal Regulation in Rice
 Plant Physiology, 2012, 160(4): 1795-1807

3. Takeshi Fukao;Elaine Yeung;Julia Bailey-Serres

 The Submergence Tolerance Regulator SUB1A Mediates Crosstalk between Submergence and Drought Tolerance in Rice
 The Plant Cell, 2011, 23(1): 412-427

4. N. P. Kudahettige;C. Pucciariello;S. Parlanti;A. Alpi;P. Perata

 Regulatory interplay of the Sub1A and CIPK15 pathways in the regulation of α-amylase production in flooded rice plants
 Plant Biology, 2011, 13(4): 611-619

5. Akman M, Bhikharie AV, McLean EH, Boonman A, Visser EJ, Schranz

 ME, van Tienderen PH(2012) Wait or escape? Contrasting submergence
 tolerance strategies of Rorippa amphibia, Rorippa sylvestrisand their hybrid. Ann Bot (Lond)109:1263–1276