Nitric oxide and protein S-nitrosylation are integral to hydrogen peroxide-induced leaf cell death in rice

Nitric oxide (NO) is a key redox-active, small molecule involved in various aspects of plant growth and development. Here, we report the identification of an NO accumulation mutant, nitric oxide excess1 (noe1), in rice (Oryza sativa), the isolation of the corresponding gene, and the analysis of its role in NO-mediated leaf cell death. Map-based cloning revealed that NOE1 encoded a rice catalase, OsCATC. Furthermore, noe1 resulted in an increase of hydrogen peroxide (H(2)O(2)) in the leaves, which consequently promoted NO production via the activation of nitrate reductase. The removal of excess NO reduced cell death in both leaves and suspension cultures derived from noe1 plants, implicating NO as an important endogenous mediator of H(2)O(2)-induced leaf cell death. Reduction of intracellular S-nitrosothiol (SNO) levels, generated by overexpression of rice S-nitrosoglutathione reductase gene (GSNOR1), which regulates global levels of protein S-nitrosylation, alleviated leaf cell death in noe1 plants. Thus, S-nitrosylation was also involved in light-dependent leaf cell death in noe1. Utilizing the biotin-switch assay, nanoliquid chromatography, and tandem mass spectrometry, S-nitrosylated proteins were identified in both wild-type and noe1 plants. NO targets identified only in noe1 plants included glyceraldehyde 3-phosphate dehydrogenase and thioredoxin, which have been reported to be involved in S-nitrosylation-regulated cell death in animals. Collectively, our data suggest that both NO and SNOs are important mediators in the process of H(2)O(2)-induced leaf cell death in rice.     

定位于类囊体膜的PPF1在转基因拟南芥中的表达影响叶绿体的发育

PPF1是一个与植物营养生长相关的基因。它编码的产物可能是一个膜蛋白并与拟南芥叶绿体中的类囊体蛋白ALB3有很高的同源性。免疫电镜分析表明PPF1蛋白同样主要定位于类囊体膜 ,而且在短日照G2豌豆开花两周后仍发育良好的叶绿体中有很高的表达 ,在长日照豌豆同时期非正常叶绿体中丰度非常低。对转基因拟南芥和野生型植株的叶片衰老进程比较发现 ,PPF1在拟南芥中的过量表达可以延缓叶片的衰老 ,而用PPF1反义mRNA抑制拟南芥中的同源基因ALB3则明显加快叶片衰老速度。对转基因拟南芥的超微结构分析显示 ,PPF1在拟南芥中过量表达时 ,转基因植株的叶绿体比野生型植株的叶绿体大并含有更多的基粒和基质类囊体膜 ;相反 ,反义PPF1表达抑制其在拟南芥中的同源物时 ,转基因植株的叶绿体比野生型植株的叶绿体小并含有较少的基粒和发育较差的类囊体膜系统。这些数据表明叶绿体的发育状况与PPF1或拟南芥同源物ALB3的表达水平呈正相关。我们的结果提示PPF1基因可能通过控制叶绿体的发育状况来调节植物的发育。     

Nitric oxide is required for an optimal establishment of the Medicago truncatula-Sinorhizobium meliloti symbiosis

Nitric oxide (NO) is a gaseous molecule that participates in numerous plant signalling pathways. It is involved in plant responses to pathogens and development processes such as seed germination, flowering and stomatal closure. Using a permeable NO-specific fluorescent probe and a bacterial reporter strain expressing the lacZ gene under the control of a NO-responsive promoter, we detected NO production in the first steps, during infection threads growth, of the Medicago truncatula-Sinorhizobium meliloti symbiotic interaction. Nitric oxide was also detected, by confocal microscopy, in nodule primordia. Depletion of NO caused by cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl-3-oxide), an NO scavenger, resulted in a significant delay in nodule appearance. The overexpression of a bacterial hmp gene, encoding a flavohaemoglobin able to scavenge NO, under the control of a nodule-specific promoter (pENOD20) in transgenic roots, led to the same phenotype. The NO scavenging resulting from these approaches provoked the downregulation of plant genes involved in nodule development, such as MtCRE1 and MtCCS52A. Furthermore, an Hmp-overexpressing S. meliloti mutant strain was found to be less competitive than the wild type in the nodulation process. Taken together, these results indicate that NO is required for an optimal establishment of the M. truncatula-S. meliloti symbiotic interaction.     

Extragenic suppressors of the Arabidopsis gai mutation alter the dose-response relationship of diverse gibberellin responses

Active gibberellins (GAs) are endogenous factors that regulate plant growth and development in a dose-dependent fashion. Mutant plants that are GA deficient, or exhibit reduced GA responses, display a characteristic dwarf phenotype. Extragenic suppressor analysis has resulted in the isolation of Arabidopsis mutations, which partially suppress the dwarf phenotype conferred by GA deficiency and reduced GA-response mutations. Here we describe detailed studies of the effects of two of these suppressors, spy-7 and gar2-1, on several different GA-responsive growth processes (seed germination, vegetative growth, stem elongation, chlorophyll accumulation, and flowering) and on the in planta amounts of active and inactive GA species. The results of these experiments show that spy-7 and gar2-1 affect the GA dose-response relationship for a wide range of GA responses and suggest that all GA-regulated processes are controlled through a negatively acting GA-signaling pathway.     

The Angiosperm Gibberellin-GID1-DELLA Growth Regulatory Mechanism: How an “Inhibitor of an Inhibitor” Enables Flexible Response to Fluctuating Environments

The phytohormone gibberellin (GA) has long been known to regulate the growth, development, and life cycle progression of flowering plants. However, the molecular GA-GID1-DELLA mechanism that enables plants to respond to GA has only recently been discovered. In addition, studies published in the last few years have highlighted previously unsuspected roles for the GA-GID1-DELLA mechanism in regulating growth response to environmental variables. Here, we review these advances within a general plant biology context and speculate on the answers to some remaining questions. We also discuss the hypothesis that the GA-GID1-DELLA mechanism enables flowering plants to maintain transient growth arrest, giving them the flexibility to survive periods of adversity.     

Cost of reproduction in the pink lady's slipper orchid (Cypripedium acaule, Orchidaceae): an eleven-year experimental study of three populations

An 11-yr experimental study of the cost of reproduction in three wild populations of the perennial orchid Cypripedium acaule contrasted experimental plants that were repeatedly hand-pollinated and often made fruits with control plants that were not hand-pollinated and only rarely made fruits. Repeated flowering without subsequent fruit production resulted in no detectable reduction in either plant size or probability of flowering in subsequent years. A cost of fruit production was evident in experimental plants in all three populations in terms of a reduced probability of flowering and smaller leaf area in subsequent years, but was not evident in terms of mortality rate. Experimental effects of fruit production reached maximum values at 3-7 yr, depending on the population. The probability of remaining dormant below ground in a given year was strongly dependent on plant size in the previous year. Furthermore, the length of the dormancy period (one to several years) was a significant and inverse function of plant size just prior to dormancy. Sample sizes and the consequent ability to detect experimental effects declined over time as more plants died or stopped flowering. Four to seven years appears to be an optimal duration for studies of the cost of reproduction in perennial herbs similar to this species. Studies lasting less than 4 yr may be too brief to reveal experimental effects, whereas those lasting more than 7 yr may fail to reveal new insights.     

Response to mild water stress in transgenic Pssu-ipt tobacco

The response of antioxidant enzymes to cyclic drought was studied in control non-transformed tobacco (Nicotiana tabacum L. cv. Petit Havana SR1) and two types of transgenic Pssu-ipt tobacco (grafted on wild rootstock and poorly rooted progeny of F1 generation) grown under different conditions of irradiation (greenhouse, referred as high light, versus growth chamber, referred as low light). Water stress cycles started with plants at two contrasting developmental stages, i.e., at the stage of vegetative growth (young) and at the onset of flowering (old). Drought reduced the growth of SR1 plants compared with transgenic ones, particularly, when treatment started in earlier stage of plant development. Relative leaf water content was significantly lower (below 70%) in all transgenic grafts and plants compared with the wild type, irrespective of age, drought, and growth conditions. The response of antioxidant enzymes was significantly dependent on plant type and plant age; nevertheless, growth conditions and water stress also affected enzyme activities. Contrary to non-transgenic tobacco, where about half of glutathione reductase activity was found in older plants, both transgenic types exhibited unchanged activities throughout plant development and stress treatment. No differences were found in catalase activity, although the growth in the greenhouse caused a moderate increase in all older plants. In contrast to non-transgenic and Pssu-ipt rooted plants, peroxidase activities (ascorbate, guaiacol, and syringaldazine peroxidase) in older Pssu-ipt grafts were up to four times higher, irrespective of growth and stress, nevertheless, the effect seemed to be age-dependent. Superoxide dismutase (SOD) activity was affected particularly by plant age but also by growth conditions. Unlike in older plants, water stress caused an increase of SOD activities in all younger plants. The differences observed in activities of enzymes of intermediary metabolism (i.e., malic enzyme and glucose-6-phosphate dehydrogenase) revealed that transgenic grafts probably compensated differently for a decrease of ATP and NADPH than control and transgenic rooted plants under stress.     

Overexpression of Rice Sphingosine-1-Phoshpate Lyase Gene OsSPL1 in Transgenic Tobacco Reduces Salt and Oxidative Stress Tolerance

Sphingolipids, including sphingosine-1-phosphate (S1P), have been shown to function as signaling mediators to regulate diverse aspects of plant growth, development, and stress response. In this study, we performed functional analysis of a rice (Oryza sativa) S1P lyase gene OsSPL1 in transgenic tobacco plants and explored its possible involvement in abiotic stress response. Overexpression of OsSPL1 in transgenic tobacco resulted in enhanced sensitivity to exogenous abscisic acid (ABA), and decreased tolerance to salt and oxidative stress, when compared with the wild type. Furthermore, the expression levels of some selected stress-related genes in OsSPL1-overexpressing plants were reduced after application of salt or oxidative stress, indicating that the altered responsiveness of stress-related genes may be responsible for the reduced tolerance in OsSPL1-overexpressing tobacco plants under salt and oxidative stress. Our results suggest that rice OsSPL1 plays an important role in abiotic stress responses.     

FIE and CURLY LEAF polycomb proteins interact in the regulation of homeobox gene expression during sporophyte development

The Arabidopsis FERTILIZATION-INDEPENDENT ENDOSPERM (FIE) polycomb group (PcG) protein, a WD40 homologue of Drosophila extra sex comb (ESC), regulates endosperm and embryo development and represses flowering during embryo and seedling development. As fie alleles are not transmitted maternally, homozygous mutant plants cannot be obtained. To study FIE function during the entire plant life cycle, we used Arabidopsis FIE co-suppressed plants. Low FIE level in these plants produced dramatic morphological aberrations, including loss of apical dominance, curled leaves, early flowering and homeotic conversion of leaves, flower organs and ovules into carpel-like structures. These morphological aberrations are similar to those exhibited by plants overexpressing AGAMOUS (AG) or CURLY LEAF (clf) mutants. Furthermore, the aberrant leaf morphology of FIE-silenced and clf plants correlates with de-repression of the class I KNOTTED-like homeobox (KNOX) genes including KNOTTED-like from Arabidopsis thaliana 2 (KNAT2) and SHOOTMERISTEMLESS (STM), whereas BREVIPEDICELLUS (BP) was upregulated in FIE-silenced plants, but not in the clf mutant. Thus, FIE is essential for the control of shoot and leaf development. Yeast two-hybrid and pull-down assays demonstrate that FIE interacts with CLF. Collectively, the morphological characteristics, together with the molecular and biochemical data presented in this work, strongly suggest that in plants, as in mammals and insects, PcG proteins control expression of homeobox genes. Our findings demonstrate that the versatility of the plant FIE function, which is derived from association with different SET (SU (VAR)3-9, E (Z), Trithorax) domain PcG proteins, results in differential regulation of gene expression throughout the plant life cycle.     

蛋白亚硝基化研究进展及其在植物抗病中的作用

蛋白亚硝基化（S-nitrosylation）是一种在一氧化氮作用下与蛋白半胱氨酸巯基共价结合,使巯基-SH转化为-SNO的反应。作为一种氧化还原依赖的翻译后调控形式,蛋白亚硝基化对多种蛋白的功能具有调节作用,越来越多的证据表明蛋白亚硝基化在植物抗病中发挥重要的作用。简要介绍了蛋白巯基亚硝基化的特点、检测方法、功能研究以及在植物抗病调节方面的最新进展。     

Phylogenomic analyses of the BARREN STALK1/LAX PANICLE1 (BA1/LAX1) genes and evidence for their roles during axillary meristem development

The diversity of plant architectural form is largely determined by the extent and duration of axillary meristem (AM) derived lateral growth. The orthologous basic helix-loop-helix (bHLH) proteins maize BARREN STALK1 (BA1) and rice LAX PANICLE1 (LAX1) are essential for the formation of AMs during vegetative development and all lateral structures during inflorescence development, but whether BA1/LAX1 co-orthologs exist outside of the grass family is unclear. Here, we present Bayesian phylogenetic evidence of a well-supported BA1/LAX1 clade comprised monocots and eudicots, estimating an origin for the lineage at least near the base of flowering plants. Genomic analyses in Arabidopsis, papaya, medicago, rice, sorghum, and maize indicate that BA1/LAX1 genes reside in syntenic regions, although there has also been a complex pattern of gene duplication and loss during the diversification of the angiosperm clade. BA1/LAX1 mRNA expression coincided with the initiation of leaves and associated AMs in the vegetative meristems of broccoli, medicago, and papaya implicating a role for the lineage in the formation of AMs in eudicots as well as monocots. Expression on the adaxial surface of lateral inflorescence structures was conserved in all sampled flowering plants, whereas mRNA expression in leaves of Arabidopsis, broccoli, and papaya also links BA1/LAX1 co-orthologs with roles in regulating leaf development, possibly as a downstream target of auxin regulating genes. Together these data point to roles for BA1/LAX1 genes during AM formation, leaf, and inflorescence development in diverse flowering plants and lend support to the hypothesis that the same genetic mechanisms regulate the development of different AM types.     

The PsbQ protein is required in Arabidopsis for photosystem II assembly/stability and photoautotrophy under low light conditions

RNA interference was used to simultaneously suppress the expression of the two genes that encode the PsbQ proteins of Photosystem II (PS II) in Arabidopsis thaliana, psbQ-1 (At4g21280) and psbQ-2 (At4g05180). Two independent PsbQ-deficient plant lines were examined. These plant lines produced little detectable PsbQ protein. Under normal growth light conditions, the wild type and mutant plants were visually indistinguishable. Additionally, analysis of steady state oxygen evolution rates and chlorophyll fluorescence characteristics indicated little alteration of photosynthetic capacity in the mutant plants. No loss of other PS II proteins was evident. Interestingly, flash oxygen yield analysis performed on thylakoid membranes isolated from the mutant and wild type plants indicated that the oxygen-evolving complex was quite unstable in the mutants. Furthermore, the lifetime of the S2 state of the oxygen-evolving complex appeared to be increased in these plants. Incubation of the wild type and mutant plants under low light growth conditions led to a significantly stronger observed phenotype in the mutants. The mutant plants progressively yellowed (after 2 weeks) and eventually died (after 3-4 weeks). The wild type plants exhibited only slight yellowing after 4 weeks under low light conditions. The mutant plants exhibited a large loss of a number of PS II components, including CP47 and the D2 protein, under low light conditions. Additionally, significant alterations of their fluorescence characteristics were observed, including an increased FO and decreased FV, yielding a large loss in PS II quantum efficiency (FV/FM). Analysis of QA- decay kinetics in the absence of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea indicated a defect in electron transfer from QA- to QB, whereas experiments performed in the presence of this herbicide indicated that the recombination rate between QA- and the S2 state was strongly retarded. These results indicate that the loss of the PsbQ protein induces significant changes in Photosystem II function, particularly in low light-grown plants, and that the PsbQ protein is required for photoautotrophic growth under low light conditions.     

拟南芥转录因子bHLH17负调控茉莉素介导的抗性反应

植物激素茉莉素作为抗性信号调控植物对腐生性病原菌和昆虫的抗性, 作为发育信号调控植物根的生长、雄蕊发育、表皮毛形成和叶片衰老。茉莉素受体COI1识别茉莉素分子, 进而与JAZ蛋白互作并诱导其降解, 继而调控多种茉莉素反应。拟南芥(Arabidopsis thaliana) IIId亚组bHLH转录因子(bHLH3、bHLH13、bHLH14和bHLH17)是JAZ的一类靶蛋白。与野生型相比, IIId亚组bHLH转录因子的单突变体对灰霉菌和甜菜夜蛾的抗性无明显差异, 而四突变体对灰霉菌和甜菜夜蛾的抗性增强。该文通过高表达bHLH17并研究其对灰霉菌和甜菜夜蛾的抗性反应, 结果显示, 被灰霉菌侵染的bHLH17高表达植株较野生型表现出更严重的病症。取食bHLH17高表达植株叶片的甜菜夜蛾幼虫体重大于取食野生型叶片的幼虫体重。bHLH17高表达抑制了茉莉素诱导的抗性相关基因(Thi2.1)和伤害响应基因(VSP2、AOS、JAZ1、JAZ9和JAZ10)的表达。原生质体转化实验显示bHLH17通过其N端行使转录抑制功能。研究结果表明, IIId亚组bHLH转录抑制因子bHLH17高表达会负调控茉莉素介导的对灰霉菌和甜菜夜蛾的抗性。     

脯氨酸参与植物开花信号转导途径

作为一种渗透调节物质,人们对脯氨酸已经有了很多的研究,然而脯氨酸在生命体生长发育中的作用还知之甚少。为了研究脯氨酸在生长发育中的作用,筛选得到了拟南芥的脯氨酸抗性突变体kao2。突变体在不同浓度脯氨酸培养基上均表现出抗性,但是突变体中脯氨酸的吸收没有显著变化,降解关键基因表达也没有增多。Tail-PCR进行突变基因克隆的结果表明,T-DNA插入位点位于AtKAO2(At2g32440)的第一个外显子,且插入导致AtKAO2基因不再表达。拟南芥突变体库中订购的kao2-2同样表现出脯氨酸抗性表型。此外,kao2表现出胁迫敏感表型。kao2表现出明显的晚花表型,并且赤霉素的添加能够部分挽救晚花表型。而kao2突变体中开花抑制因子FLC表达升高,而开花促进基因FT的表达降低。研究在脯氨酸与开花信号转导途径之间建立了联系,为脯氨酸对开花途径的信号作用提供了新的证据,为以后的研究提供了新的材料。     

Elevated pCO(2 )favours nitrate reduction in the roots of wild-type tobacco (Nicotiana tabacum cv. Gat.) and significantly alters N-metabolism in transformants lacking functional nitrate reductase in the roots

The impact of elevated pCO(2 )on N-metabolism of hydroponically grown wild-type and transformed tobacco plants lacking root nitrate reduction was studied in order to elucidate the effects on (i) nitrate uptake, (ii) long-distance transport of N, (iii) nitrate reduction with emphasis on root-NR, and (iv) the allocation of N between the root and shoot. The findings were related to alterations of growth rates. At elevated pCO(2 )the wild type exhibited higher growth rates, which were accompanied by an increase of NO(3)(-)-uptake per plant, due to a higher root:shoot ratio. Furthermore, elevated pCO(2 )enhanced nitrate reduction in the roots of the wild type, resulting in enhanced xylem-loading of organic N (amino-N) to supply the shoot with sufficient nitrogen, and decreased phloem-transport of organic N in a basipetal direction. Transformed tobacco plants lacking root nitrate reduction were smaller than the wild type and exhibited lower growth rates. Nitrate uptake per plant was decreased in transformed plants as a consequence of an impeded root growth and, thus, a significantly decreased root:shoot ratio. Surprisingly, transformed plants showed an altered allocation of amino-N between the root and the shoot, with an increase of amino-N in the root and a substantial decrease of amino-N in the shoot. In transformed plants, xylem-loading of nitrate was increased and the roots were supplied with organic N via phloem transport. Elevated pCO(2 )increased shoot-NR, but only slightly affected the growth rates of transformed plants, whereas carbohydrates accumulated at elevated pCO(2 )as indicated by a significant increase of the C/N ratio in the leaves of transformed plants. Unexpectedly, the C/N balance and the functional equilibrium between root and shoot growth was disturbed dramatically by the loss of nitrate reduction in the root.     

Brassinosteroids regulate glucosinolate biosynthesis in Arabidopsis thaliana

Plants must constantly adjust their growth and defense responses to deal with the wide variety of stresses they encounter in their environment. Among phytohormones, brassinosteroids (BRs) are an important group of plant steroid hormones involved in numerous aspects of the plant lifecycle including growth, development and responses to various stresses including insect attacks. Here, we show that BRs regulate glucosinolate (GS) biosynthesis and function in insect herbivory. Preference tests and larval feeding experiments using the generalist herbivore, diamondback moth (Plutella xylostella), revealed that the larvae prefer to feed on Arabidopsis thaliana brassinosteroid insensitive 1 (bri1‐5) plants over wild‐type Ws‐2 or BRI1‐Flag (bri1‐5 background) transgenic plants, which results in an increase in larval weight. Analysis of GS contents showed that 3‐(methylsulfinyl) propyl GS (C3) levels were higher in bri1‐5 than in Ws2 and BRI1‐Flag transgenic plants, whereas sinigrin (2‐propenylglucosinolate), glucoerucin (4‐methylthiobutylglucosinolate) and glucobrassicin (indol‐3‐ylmethylglucosinolate) levels were lower in this mutant. We investigated the effect of brassinolide (BL) on GS biosynthesis in Arabidopsis and radish (Raphanus sativus L.) by monitoring the expression levels of GS biosynthetic genes, including MAM1, MAM3, BCAT4 and AOP2, which increased in a BL‐dependent manner. These results suggest that BRs regulate GS profiles in higher plants, which function in defense responses against insects.     

Inactivation of genes,encoding tocopherol biosynthetic pathway enzymes,results in oxidative stress in outdoor grown Arabidopsis thaliana

Tocopherols (α-, β-, γ- and δ-tocopherols) represent a group of lipophilic antioxidants which are synthesized only by photosynthetic organisms. It is widely believed that protection of pigments and proteins of photosynthetic system and polyunsaturated fatty acids from oxidative damage caused by reactive oxygen species (ROS) is the main function of tocopherols. The wild type Columbia and two mutants of Arabidopsis thaliana with T-DNA insertions in tocopherol biosynthesis genes – tocopherol cyclase (vte1) and γ-tocopherol methyltransferase (vte4) – were analyzed after long-term outdoor growth. The concentration of total tocopherol was up to 12-fold higher in outdoor growing wild type and vte4 plant lines than in plants grown under laboratory conditions. The vte4 mutant plants had a lower concentration of chlorophylls and carotenoids, whereas the mutant plants had a higher level of total glutathione than of wild type. The activities of antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate oxidase (AO, EC 1.10.3.3) were lower in both mutants, whereas activities of catalase (EC 1.11.1.6) and ascorbate peroxidase (APx, EC 1.11.1.11) were lower only in vte1 mutant plants in comparison to wild type plants. However, the activity of guaiacol peroxidase (GuPx, EC 1.11.1.7) was higher in vte1 and vte4 mutants than that in wild type. Additionally, both mutant plant lines had higher concentration of protein carbonyl groups and oxidized glutathione compared to the wild type, indicating the development of oxidative stress. These results demonstrate in plants that tocopherols play a crucial role for growth of plants under outdoor conditions by preventing oxidation of cellular components.     

Overexpression of a Medicago truncatula stress-associated protein gene (MtSAP1) leads to nitric oxide accumulation and confers osmotic and salt stress tolerance in transgenic tobacco

The impact of Medicago truncatula stress-associated protein gene (MtSAP1) overexpression has been investigated in Nicotiana tabacum transgenic seedlings. Under optimal conditions, transgenic lines overexpressing MtSAP1 revealed better plant development and higher chlorophyll content as compared to wild type seedlings. Interestingly, transgenic lines showed a stronger accumulation of nitric oxide (NO), a signaling molecule involved in growth and development processes. This NO production seemed to be partially nitrate reductase dependent. Due to the fact that NO has been also reported to play a role in tolerance acquisition of plants to abiotic stresses, the responses of MtSAP1 overexpressors to osmotic and salt stress have been studied. Compared to the wild type, transgenic lines were less affected in their growth and development. Moreover, NO content in MtSAP1 overexpressors was always higher than that detected in wild seedlings under stress conditions. It seems that this better tolerance induced by MtSAP1 overexpression could be associated with this higher NO production that would enable seedlings to reach a high protection level to prepare them to cope with abiotic stresses.